Trait rayon::iter::ParallelIterator

source ·

pub trait ParallelIterator: Sized + Send {
    type Item: Send;

Show 54 methods    // Required method
    fn drive_unindexed<C>(self, consumer: C) -> C::Result
       where C: UnindexedConsumer<Self::Item>;

    // Provided methods
    fn for_each<OP>(self, op: OP)
       where OP: Fn(Self::Item) + Sync + Send { ... }
    fn for_each_with<OP, T>(self, init: T, op: OP)
       where OP: Fn(&mut T, Self::Item) + Sync + Send,
             T: Send + Clone { ... }
    fn for_each_init<OP, INIT, T>(self, init: INIT, op: OP)
       where OP: Fn(&mut T, Self::Item) + Sync + Send,
             INIT: Fn() -> T + Sync + Send { ... }
    fn try_for_each<OP, R>(self, op: OP) -> R
       where OP: Fn(Self::Item) -> R + Sync + Send,
             R: Try<Ok = ()> + Send { ... }
    fn try_for_each_with<OP, T, R>(self, init: T, op: OP) -> R
       where OP: Fn(&mut T, Self::Item) -> R + Sync + Send,
             T: Send + Clone,
             R: Try<Ok = ()> + Send { ... }
    fn try_for_each_init<OP, INIT, T, R>(self, init: INIT, op: OP) -> R
       where OP: Fn(&mut T, Self::Item) -> R + Sync + Send,
             INIT: Fn() -> T + Sync + Send,
             R: Try<Ok = ()> + Send { ... }
    fn count(self) -> usize { ... }
    fn map<F, R>(self, map_op: F) -> Map<Self, F>
       where F: Fn(Self::Item) -> R + Sync + Send,
             R: Send { ... }
    fn map_with<F, T, R>(self, init: T, map_op: F) -> MapWith<Self, T, F>
       where F: Fn(&mut T, Self::Item) -> R + Sync + Send,
             T: Send + Clone,
             R: Send { ... }
    fn map_init<F, INIT, T, R>(
        self,
        init: INIT,
        map_op: F,
    ) -> MapInit<Self, INIT, F>
       where F: Fn(&mut T, Self::Item) -> R + Sync + Send,
             INIT: Fn() -> T + Sync + Send,
             R: Send { ... }
    fn cloned<'a, T>(self) -> Cloned<Self>
       where T: 'a + Clone + Send,
             Self: ParallelIterator<Item = &'a T> { ... }
    fn copied<'a, T>(self) -> Copied<Self>
       where T: 'a + Copy + Send,
             Self: ParallelIterator<Item = &'a T> { ... }
    fn inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP>
       where OP: Fn(&Self::Item) + Sync + Send { ... }
    fn update<F>(self, update_op: F) -> Update<Self, F>
       where F: Fn(&mut Self::Item) + Sync + Send { ... }
    fn filter<P>(self, filter_op: P) -> Filter<Self, P>
       where P: Fn(&Self::Item) -> bool + Sync + Send { ... }
    fn filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P>
       where P: Fn(Self::Item) -> Option<R> + Sync + Send,
             R: Send { ... }
    fn flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F>
       where F: Fn(Self::Item) -> PI + Sync + Send,
             PI: IntoParallelIterator { ... }
    fn flat_map_iter<F, SI>(self, map_op: F) -> FlatMapIter<Self, F>
       where F: Fn(Self::Item) -> SI + Sync + Send,
             SI: IntoIterator,
             SI::Item: Send { ... }
    fn flatten(self) -> Flatten<Self>
       where Self::Item: IntoParallelIterator { ... }
    fn flatten_iter(self) -> FlattenIter<Self>
       where Self::Item: IntoIterator,
             <Self::Item as IntoIterator>::Item: Send { ... }
    fn reduce<OP, ID>(self, identity: ID, op: OP) -> Self::Item
       where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,
             ID: Fn() -> Self::Item + Sync + Send { ... }
    fn reduce_with<OP>(self, op: OP) -> Option<Self::Item>
       where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send { ... }
    fn try_reduce<T, OP, ID>(self, identity: ID, op: OP) -> Self::Item
       where OP: Fn(T, T) -> Self::Item + Sync + Send,
             ID: Fn() -> T + Sync + Send,
             Self::Item: Try<Ok = T> { ... }
    fn try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item>
       where OP: Fn(T, T) -> Self::Item + Sync + Send,
             Self::Item: Try<Ok = T> { ... }
    fn fold<T, ID, F>(self, identity: ID, fold_op: F) -> Fold<Self, ID, F>
       where F: Fn(T, Self::Item) -> T + Sync + Send,
             ID: Fn() -> T + Sync + Send,
             T: Send { ... }
    fn fold_with<F, T>(self, init: T, fold_op: F) -> FoldWith<Self, T, F>
       where F: Fn(T, Self::Item) -> T + Sync + Send,
             T: Send + Clone { ... }
    fn try_fold<T, R, ID, F>(
        self,
        identity: ID,
        fold_op: F,
    ) -> TryFold<Self, R, ID, F>
       where F: Fn(T, Self::Item) -> R + Sync + Send,
             ID: Fn() -> T + Sync + Send,
             R: Try<Ok = T> + Send { ... }
    fn try_fold_with<F, T, R>(
        self,
        init: T,
        fold_op: F,
    ) -> TryFoldWith<Self, R, F>
       where F: Fn(T, Self::Item) -> R + Sync + Send,
             R: Try<Ok = T> + Send,
             T: Clone + Send { ... }
    fn sum<S>(self) -> S
       where S: Send + Sum<Self::Item> + Sum<S> { ... }
    fn product<P>(self) -> P
       where P: Send + Product<Self::Item> + Product<P> { ... }
    fn min(self) -> Option<Self::Item>
       where Self::Item: Ord { ... }
    fn min_by<F>(self, f: F) -> Option<Self::Item>
       where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering { ... }
    fn min_by_key<K, F>(self, f: F) -> Option<Self::Item>
       where K: Ord + Send,
             F: Sync + Send + Fn(&Self::Item) -> K { ... }
    fn max(self) -> Option<Self::Item>
       where Self::Item: Ord { ... }
    fn max_by<F>(self, f: F) -> Option<Self::Item>
       where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering { ... }
    fn max_by_key<K, F>(self, f: F) -> Option<Self::Item>
       where K: Ord + Send,
             F: Sync + Send + Fn(&Self::Item) -> K { ... }
    fn chain<C>(self, chain: C) -> Chain<Self, C::Iter>
       where C: IntoParallelIterator<Item = Self::Item> { ... }
    fn find_any<P>(self, predicate: P) -> Option<Self::Item>
       where P: Fn(&Self::Item) -> bool + Sync + Send { ... }
    fn find_first<P>(self, predicate: P) -> Option<Self::Item>
       where P: Fn(&Self::Item) -> bool + Sync + Send { ... }
    fn find_last<P>(self, predicate: P) -> Option<Self::Item>
       where P: Fn(&Self::Item) -> bool + Sync + Send { ... }
    fn find_map_any<P, R>(self, predicate: P) -> Option<R>
       where P: Fn(Self::Item) -> Option<R> + Sync + Send,
             R: Send { ... }
    fn find_map_first<P, R>(self, predicate: P) -> Option<R>
       where P: Fn(Self::Item) -> Option<R> + Sync + Send,
             R: Send { ... }
    fn find_map_last<P, R>(self, predicate: P) -> Option<R>
       where P: Fn(Self::Item) -> Option<R> + Sync + Send,
             R: Send { ... }
    fn any<P>(self, predicate: P) -> bool
       where P: Fn(Self::Item) -> bool + Sync + Send { ... }
    fn all<P>(self, predicate: P) -> bool
       where P: Fn(Self::Item) -> bool + Sync + Send { ... }
    fn while_some<T>(self) -> WhileSome<Self>
       where Self: ParallelIterator<Item = Option<T>>,
             T: Send { ... }
    fn panic_fuse(self) -> PanicFuse<Self> { ... }
    fn collect<C>(self) -> C
       where C: FromParallelIterator<Self::Item> { ... }
    fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
       where Self: ParallelIterator<Item = (A, B)>,
             FromA: Default + Send + ParallelExtend<A>,
             FromB: Default + Send + ParallelExtend<B>,
             A: Send,
             B: Send { ... }
    fn partition<A, B, P>(self, predicate: P) -> (A, B)
       where A: Default + Send + ParallelExtend<Self::Item>,
             B: Default + Send + ParallelExtend<Self::Item>,
             P: Fn(&Self::Item) -> bool + Sync + Send { ... }
    fn partition_map<A, B, P, L, R>(self, predicate: P) -> (A, B)
       where A: Default + Send + ParallelExtend<L>,
             B: Default + Send + ParallelExtend<R>,
             P: Fn(Self::Item) -> Either<L, R> + Sync + Send,
             L: Send,
             R: Send { ... }
    fn intersperse(self, element: Self::Item) -> Intersperse<Self>
       where Self::Item: Clone { ... }
    fn opt_len(&self) -> Option<usize> { ... }
}

Expand description

Parallel version of the standard iterator trait.

The combinators on this trait are available on all parallel iterators. Additional methods can be found on the IndexedParallelIterator trait: those methods are only available for parallel iterators where the number of items is known in advance (so, e.g., after invoking filter, those methods become unavailable).

For examples of using parallel iterators, see the docs on the iter module.

Required Associated Types§

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type Item: Send

The type of item that this parallel iterator produces. For example, if you use the for_each method, this is the type of item that your closure will be invoked with.

Required Methods§

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fn drive_unindexed<C>(self, consumer: C) -> C::Result
where C: UnindexedConsumer<Self::Item>,

Internal method used to define the behavior of this parallel iterator. You should not need to call this directly.

This method causes the iterator self to start producing items and to feed them to the consumer consumer one by one. It may split the consumer before doing so to create the opportunity to produce in parallel.

See the README for more details on the internals of parallel iterators.

Provided Methods§

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fn for_each<OP>(self, op: OP)
where OP: Fn(Self::Item) + Sync + Send,

Executes OP on each item produced by the iterator, in parallel.

§Examples

use rayon::prelude::*;

(0..100).into_par_iter().for_each(|x| println!("{:?}", x));

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fn for_each_with<OP, T>(self, init: T, op: OP)
where OP: Fn(&mut T, Self::Item) + Sync + Send, T: Send + Clone,

Executes OP on the given init value with each item produced by the iterator, in parallel.

The init value will be cloned only as needed to be paired with the group of items in each rayon job. It does not require the type to be Sync.

§Examples

use std::sync::mpsc::channel;
use rayon::prelude::*;

let (sender, receiver) = channel();

(0..5).into_par_iter().for_each_with(sender, |s, x| s.send(x).unwrap());

let mut res: Vec<_> = receiver.iter().collect();

res.sort();

assert_eq!(&res[..], &[0, 1, 2, 3, 4])

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fn for_each_init<OP, INIT, T>(self, init: INIT, op: OP)
where OP: Fn(&mut T, Self::Item) + Sync + Send, INIT: Fn() -> T + Sync + Send,

Executes OP on a value returned by init with each item produced by the iterator, in parallel.

The init function will be called only as needed for a value to be paired with the group of items in each rayon job. There is no constraint on that returned type at all!

§Examples

use rand::Rng;
use rayon::prelude::*;

let mut v = vec![0u8; 1_000_000];

v.par_chunks_mut(1000)
    .for_each_init(
        || rand::thread_rng(),
        |rng, chunk| rng.fill(chunk),
    );

// There's a remote chance that this will fail...
for i in 0u8..=255 {
    assert!(v.contains(&i));
}

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fn try_for_each<OP, R>(self, op: OP) -> R
where OP: Fn(Self::Item) -> R + Sync + Send, R: Try<Ok = ()> + Send,

Executes a fallible OP on each item produced by the iterator, in parallel.

If the OP returns Result::Err or Option::None, we will attempt to stop processing the rest of the items in the iterator as soon as possible, and we will return that terminating value. Otherwise, we will return an empty Result::Ok(()) or Option::Some(()). If there are multiple errors in parallel, it is not specified which will be returned.

§Examples

use rayon::prelude::*;
use std::io::{self, Write};

// This will stop iteration early if there's any write error, like
// having piped output get closed on the other end.
(0..100).into_par_iter()
    .try_for_each(|x| writeln!(io::stdout(), "{:?}", x))
    .expect("expected no write errors");

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fn try_for_each_with<OP, T, R>(self, init: T, op: OP) -> R
where OP: Fn(&mut T, Self::Item) -> R + Sync + Send, T: Send + Clone, R: Try<Ok = ()> + Send,

Executes a fallible OP on the given init value with each item produced by the iterator, in parallel.

This combines the init semantics of for_each_with() and the failure semantics of try_for_each().

§Examples

use std::sync::mpsc::channel;
use rayon::prelude::*;

let (sender, receiver) = channel();

(0..5).into_par_iter()
    .try_for_each_with(sender, |s, x| s.send(x))
    .expect("expected no send errors");

let mut res: Vec<_> = receiver.iter().collect();

res.sort();

assert_eq!(&res[..], &[0, 1, 2, 3, 4])

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fn try_for_each_init<OP, INIT, T, R>(self, init: INIT, op: OP) -> R
where OP: Fn(&mut T, Self::Item) -> R + Sync + Send, INIT: Fn() -> T + Sync + Send, R: Try<Ok = ()> + Send,

Executes a fallible OP on a value returned by init with each item produced by the iterator, in parallel.

This combines the init semantics of for_each_init() and the failure semantics of try_for_each().

§Examples

use rand::Rng;
use rayon::prelude::*;

let mut v = vec![0u8; 1_000_000];

v.par_chunks_mut(1000)
    .try_for_each_init(
        || rand::thread_rng(),
        |rng, chunk| rng.try_fill(chunk),
    )
    .expect("expected no rand errors");

// There's a remote chance that this will fail...
for i in 0u8..=255 {
    assert!(v.contains(&i));
}

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fn count(self) -> usize

Counts the number of items in this parallel iterator.

§Examples

use rayon::prelude::*;

let count = (0..100).into_par_iter().count();

assert_eq!(count, 100);

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fn map<F, R>(self, map_op: F) -> Map<Self, F>
where F: Fn(Self::Item) -> R + Sync + Send, R: Send,

Applies map_op to each item of this iterator, producing a new iterator with the results.

§Examples

use rayon::prelude::*;

let mut par_iter = (0..5).into_par_iter().map(|x| x * 2);

let doubles: Vec<_> = par_iter.collect();

assert_eq!(&doubles[..], &[0, 2, 4, 6, 8]);

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fn map_with<F, T, R>(self, init: T, map_op: F) -> MapWith<Self, T, F>
where F: Fn(&mut T, Self::Item) -> R + Sync + Send, T: Send + Clone, R: Send,

Applies map_op to the given init value with each item of this iterator, producing a new iterator with the results.

The init value will be cloned only as needed to be paired with the group of items in each rayon job. It does not require the type to be Sync.

§Examples

use std::sync::mpsc::channel;
use rayon::prelude::*;

let (sender, receiver) = channel();

let a: Vec<_> = (0..5)
                .into_par_iter()            // iterating over i32
                .map_with(sender, |s, x| {
                    s.send(x).unwrap();     // sending i32 values through the channel
                    x                       // returning i32
                })
                .collect();                 // collecting the returned values into a vector

let mut b: Vec<_> = receiver.iter()         // iterating over the values in the channel
                            .collect();     // and collecting them
b.sort();

assert_eq!(a, b);

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fn map_init<F, INIT, T, R>( self, init: INIT, map_op: F, ) -> MapInit<Self, INIT, F>
where F: Fn(&mut T, Self::Item) -> R + Sync + Send, INIT: Fn() -> T + Sync + Send, R: Send,

Applies map_op to a value returned by init with each item of this iterator, producing a new iterator with the results.

The init function will be called only as needed for a value to be paired with the group of items in each rayon job. There is no constraint on that returned type at all!

§Examples

use rand::Rng;
use rayon::prelude::*;

let a: Vec<_> = (1i32..1_000_000)
    .into_par_iter()
    .map_init(
        || rand::thread_rng(),  // get the thread-local RNG
        |rng, x| if rng.gen() { // randomly negate items
            -x
        } else {
            x
        },
    ).collect();

// There's a remote chance that this will fail...
assert!(a.iter().any(|&x| x < 0));
assert!(a.iter().any(|&x| x > 0));

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fn cloned<'a, T>(self) -> Cloned<Self>
where T: 'a + Clone + Send, Self: ParallelIterator<Item = &'a T>,

Creates an iterator which clones all of its elements. This may be useful when you have an iterator over &T, but you need T, and that type implements Clone. See also copied().

§Examples

use rayon::prelude::*;

let a = [1, 2, 3];

let v_cloned: Vec<_> = a.par_iter().cloned().collect();

// cloned is the same as .map(|&x| x), for integers
let v_map: Vec<_> = a.par_iter().map(|&x| x).collect();

assert_eq!(v_cloned, vec![1, 2, 3]);
assert_eq!(v_map, vec![1, 2, 3]);

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fn copied<'a, T>(self) -> Copied<Self>
where T: 'a + Copy + Send, Self: ParallelIterator<Item = &'a T>,

Creates an iterator which copies all of its elements. This may be useful when you have an iterator over &T, but you need T, and that type implements Copy. See also cloned().

§Examples

use rayon::prelude::*;

let a = [1, 2, 3];

let v_copied: Vec<_> = a.par_iter().copied().collect();

// copied is the same as .map(|&x| x), for integers
let v_map: Vec<_> = a.par_iter().map(|&x| x).collect();

assert_eq!(v_copied, vec![1, 2, 3]);
assert_eq!(v_map, vec![1, 2, 3]);

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fn inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP>
where OP: Fn(&Self::Item) + Sync + Send,

Applies inspect_op to a reference to each item of this iterator, producing a new iterator passing through the original items. This is often useful for debugging to see what’s happening in iterator stages.

§Examples

use rayon::prelude::*;

let a = [1, 4, 2, 3];

// this iterator sequence is complex.
let sum = a.par_iter()
            .cloned()
            .filter(|&x| x % 2 == 0)
            .reduce(|| 0, |sum, i| sum + i);

println!("{}", sum);

// let's add some inspect() calls to investigate what's happening
let sum = a.par_iter()
            .cloned()
            .inspect(|x| println!("about to filter: {}", x))
            .filter(|&x| x % 2 == 0)
            .inspect(|x| println!("made it through filter: {}", x))
            .reduce(|| 0, |sum, i| sum + i);

println!("{}", sum);

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fn update<F>(self, update_op: F) -> Update<Self, F>
where F: Fn(&mut Self::Item) + Sync + Send,

Mutates each item of this iterator before yielding it.

§Examples

use rayon::prelude::*;

let par_iter = (0..5).into_par_iter().update(|x| {*x *= 2;});

let doubles: Vec<_> = par_iter.collect();

assert_eq!(&doubles[..], &[0, 2, 4, 6, 8]);

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fn filter(self, filter_op: P) -> Filter<Self, P>
where P: Fn(&Self::Item) -> bool + Sync + Send,

Applies filter_op to each item of this iterator, producing a new iterator with only the items that gave true results.

§Examples

use rayon::prelude::*;

let mut par_iter = (0..10).into_par_iter().filter(|x| x % 2 == 0);

let even_numbers: Vec<_> = par_iter.collect();

assert_eq!(&even_numbers[..], &[0, 2, 4, 6, 8]);

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fn filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

Applies filter_op to each item of this iterator to get an Option, producing a new iterator with only the items from Some results.

§Examples

use rayon::prelude::*;

let mut par_iter = (0..10).into_par_iter()
                        .filter_map(|x| {
                            if x % 2 == 0 { Some(x * 3) }
                            else { None }
                        });

let even_numbers: Vec<_> = par_iter.collect();

assert_eq!(&even_numbers[..], &[0, 6, 12, 18, 24]);

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fn flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F>
where F: Fn(Self::Item) -> PI + Sync + Send, PI: IntoParallelIterator,

Applies map_op to each item of this iterator to get nested parallel iterators, producing a new parallel iterator that flattens these back into one.

§Examples

use rayon::prelude::*;

let a = [[1, 2], [3, 4], [5, 6], [7, 8]];

let par_iter = a.par_iter().cloned().flat_map(|a| a.to_vec());

let vec: Vec<_> = par_iter.collect();

assert_eq!(&vec[..], &[1, 2, 3, 4, 5, 6, 7, 8]);

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fn flat_map_iter<F, SI>(self, map_op: F) -> FlatMapIter<Self, F>
where F: Fn(Self::Item) -> SI + Sync + Send, SI: IntoIterator, SI::Item: Send,

Applies map_op to each item of this iterator to get nested serial iterators, producing a new parallel iterator that flattens these back into one.

§`flat_map_iter` versus `flat_map`

These two methods are similar but behave slightly differently. With flat_map, each of the nested iterators must be a parallel iterator, and they will be further split up with nested parallelism. With flat_map_iter, each nested iterator is a sequential Iterator, and we only parallelize between them, while the items produced by each nested iterator are processed sequentially.

When choosing between these methods, consider whether nested parallelism suits the potential iterators at hand. If there’s little computation involved, or its length is much less than the outer parallel iterator, then it may perform better to avoid the overhead of parallelism, just flattening sequentially with flat_map_iter. If there is a lot of computation, potentially outweighing the outer parallel iterator, then the nested parallelism of flat_map may be worthwhile.

§Examples

use rayon::prelude::*;
use std::cell::RefCell;

let a = [[1, 2], [3, 4], [5, 6], [7, 8]];

let par_iter = a.par_iter().flat_map_iter(|a| {
    // The serial iterator doesn't have to be thread-safe, just its items.
    let cell_iter = RefCell::new(a.iter().cloned());
    std::iter::from_fn(move || cell_iter.borrow_mut().next())
});

let vec: Vec<_> = par_iter.collect();

assert_eq!(&vec[..], &[1, 2, 3, 4, 5, 6, 7, 8]);

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fn flatten(self) -> Flatten<Self>
where Self::Item: IntoParallelIterator,

An adaptor that flattens parallel-iterable Items into one large iterator.

§Examples

use rayon::prelude::*;

let x: Vec<Vec<_>> = vec![vec![1, 2], vec![3, 4]];
let y: Vec<_> = x.into_par_iter().flatten().collect();

assert_eq!(y, vec![1, 2, 3, 4]);

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fn flatten_iter(self) -> FlattenIter<Self>
where Self::Item: IntoIterator, <Self::Item as IntoIterator>::Item: Send,

An adaptor that flattens serial-iterable Items into one large iterator.

See also flatten and the analagous comparison of flat_map_iter versus flat_map.

§Examples

use rayon::prelude::*;

let x: Vec<Vec<_>> = vec![vec![1, 2], vec![3, 4]];
let iters: Vec<_> = x.into_iter().map(Vec::into_iter).collect();
let y: Vec<_> = iters.into_par_iter().flatten_iter().collect();

assert_eq!(y, vec![1, 2, 3, 4]);

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fn reduce<OP, ID>(self, identity: ID, op: OP) -> Self::Item
where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send, ID: Fn() -> Self::Item + Sync + Send,

Reduces the items in the iterator into one item using op. The argument identity should be a closure that can produce “identity” value which may be inserted into the sequence as needed to create opportunities for parallel execution. So, for example, if you are doing a summation, then identity() ought to produce something that represents the zero for your type (but consider just calling sum() in that case).

§Examples

// Iterate over a sequence of pairs `(x0, y0), ..., (xN, yN)`
// and use reduce to compute one pair `(x0 + ... + xN, y0 + ... + yN)`
// where the first/second elements are summed separately.
use rayon::prelude::*;
let sums = [(0, 1), (5, 6), (16, 2), (8, 9)]
           .par_iter()        // iterating over &(i32, i32)
           .cloned()          // iterating over (i32, i32)
           .reduce(|| (0, 0), // the "identity" is 0 in both columns
                   |a, b| (a.0 + b.0, a.1 + b.1));
assert_eq!(sums, (0 + 5 + 16 + 8, 1 + 6 + 2 + 9));

Note: unlike a sequential fold operation, the order in which op will be applied to reduce the result is not fully specified. So op should be associative or else the results will be non-deterministic. And of course identity() should produce a true identity.

source

fn reduce_with<OP>(self, op: OP) -> Option<Self::Item>
where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,

Reduces the items in the iterator into one item using op. If the iterator is empty, None is returned; otherwise, Some is returned.

This version of reduce is simple but somewhat less efficient. If possible, it is better to call reduce(), which requires an identity element.

§Examples

use rayon::prelude::*;
let sums = [(0, 1), (5, 6), (16, 2), (8, 9)]
           .par_iter()        // iterating over &(i32, i32)
           .cloned()          // iterating over (i32, i32)
           .reduce_with(|a, b| (a.0 + b.0, a.1 + b.1))
           .unwrap();
assert_eq!(sums, (0 + 5 + 16 + 8, 1 + 6 + 2 + 9));

Note: unlike a sequential fold operation, the order in which op will be applied to reduce the result is not fully specified. So op should be associative or else the results will be non-deterministic.

source

fn try_reduce<T, OP, ID>(self, identity: ID, op: OP) -> Self::Item
where OP: Fn(T, T) -> Self::Item + Sync + Send, ID: Fn() -> T + Sync + Send, Self::Item: Try<Ok = T>,

Reduces the items in the iterator into one item using a fallible op. The identity argument is used the same way as in reduce().

If a Result::Err or Option::None item is found, or if op reduces to one, we will attempt to stop processing the rest of the items in the iterator as soon as possible, and we will return that terminating value. Otherwise, we will return the final reduced Result::Ok(T) or Option::Some(T). If there are multiple errors in parallel, it is not specified which will be returned.

§Examples

use rayon::prelude::*;

// Compute the sum of squares, being careful about overflow.
fn sum_squares<I: IntoParallelIterator<Item = i32>>(iter: I) -> Option<i32> {
    iter.into_par_iter()
        .map(|i| i.checked_mul(i))            // square each item,
        .try_reduce(|| 0, i32::checked_add)   // and add them up!
}
assert_eq!(sum_squares(0..5), Some(0 + 1 + 4 + 9 + 16));

// The sum might overflow
assert_eq!(sum_squares(0..10_000), None);

// Or the squares might overflow before it even reaches `try_reduce`
assert_eq!(sum_squares(1_000_000..1_000_001), None);

source

fn try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item>
where OP: Fn(T, T) -> Self::Item + Sync + Send, Self::Item: Try<Ok = T>,

Reduces the items in the iterator into one item using a fallible op.

Like reduce_with(), if the iterator is empty, None is returned; otherwise, Some is returned. Beyond that, it behaves like try_reduce() for handling Err/None.

For instance, with Option items, the return value may be:

None, the iterator was empty
Some(None), we stopped after encountering None.
Some(Some(x)), the entire iterator reduced to x.

With Result items, the nesting is more obvious:

None, the iterator was empty
Some(Err(e)), we stopped after encountering an error e.
Some(Ok(x)), the entire iterator reduced to x.

§Examples

use rayon::prelude::*;

let files = ["/dev/null", "/does/not/exist"];

// Find the biggest file
files.into_par_iter()
    .map(|path| std::fs::metadata(path).map(|m| (path, m.len())))
    .try_reduce_with(|a, b| {
        Ok(if a.1 >= b.1 { a } else { b })
    })
    .expect("Some value, since the iterator is not empty")
    .expect_err("not found");

source

fn fold<T, ID, F>(self, identity: ID, fold_op: F) -> Fold<Self, ID, F>
where F: Fn(T, Self::Item) -> T + Sync + Send, ID: Fn() -> T + Sync + Send, T: Send,

Parallel fold is similar to sequential fold except that the sequence of items may be subdivided before it is folded. Consider a list of numbers like 22 3 77 89 46. If you used sequential fold to add them (fold(0, |a,b| a+b), you would wind up first adding 0 + 22, then 22 + 3, then 25 + 77, and so forth. The parallel fold works similarly except that it first breaks up your list into sublists, and hence instead of yielding up a single sum at the end, it yields up multiple sums. The number of results is nondeterministic, as is the point where the breaks occur.

So if did the same parallel fold (fold(0, |a,b| a+b)) on our example list, we might wind up with a sequence of two numbers, like so:

22 3 77 89 46
      |     |
    102   135

Or perhaps these three numbers:

22 3 77 89 46
      |  |  |
    102 89 46

In general, Rayon will attempt to find good breaking points that keep all of your cores busy.

§Fold versus reduce

The fold() and reduce() methods each take an identity element and a combining function, but they operate rather differently.

reduce() requires that the identity function has the same type as the things you are iterating over, and it fully reduces the list of items into a single item. So, for example, imagine we are iterating over a list of bytes bytes: [128_u8, 64_u8, 64_u8]. If we used bytes.reduce(|| 0_u8, |a: u8, b: u8| a + b), we would get an overflow. This is because 0, a, and b here are all bytes, just like the numbers in the list (I wrote the types explicitly above, but those are the only types you can use). To avoid the overflow, we would need to do something like bytes.map(|b| b as u32).reduce(|| 0, |a, b| a + b), in which case our result would be 256.

In contrast, with fold(), the identity function does not have to have the same type as the things you are iterating over, and you potentially get back many results. So, if we continue with the bytes example from the previous paragraph, we could do bytes.fold(|| 0_u32, |a, b| a + (b as u32)) to convert our bytes into u32. And of course we might not get back a single sum.

There is a more subtle distinction as well, though it’s actually implied by the above points. When you use reduce(), your reduction function is sometimes called with values that were never part of your original parallel iterator (for example, both the left and right might be a partial sum). With fold(), in contrast, the left value in the fold function is always the accumulator, and the right value is always from your original sequence.

§Fold vs Map/Reduce

Fold makes sense if you have some operation where it is cheaper to create groups of elements at a time. For example, imagine collecting characters into a string. If you were going to use map/reduce, you might try this:

use rayon::prelude::*;

let s =
    ['a', 'b', 'c', 'd', 'e']
    .par_iter()
    .map(|c: &char| format!("{}", c))
    .reduce(|| String::new(),
            |mut a: String, b: String| { a.push_str(&b); a });

assert_eq!(s, "abcde");

Because reduce produces the same type of element as its input, you have to first map each character into a string, and then you can reduce them. This means we create one string per element in our iterator – not so great. Using fold, we can do this instead:

use rayon::prelude::*;

let s =
    ['a', 'b', 'c', 'd', 'e']
    .par_iter()
    .fold(|| String::new(),
            |mut s: String, c: &char| { s.push(*c); s })
    .reduce(|| String::new(),
            |mut a: String, b: String| { a.push_str(&b); a });

assert_eq!(s, "abcde");

Now fold will process groups of our characters at a time, and we only make one string per group. We should wind up with some small-ish number of strings roughly proportional to the number of CPUs you have (it will ultimately depend on how busy your processors are). Note that we still need to do a reduce afterwards to combine those groups of strings into a single string.

You could use a similar trick to save partial results (e.g., a cache) or something similar.

§Combining fold with other operations

You can combine fold with reduce if you want to produce a single value. This is then roughly equivalent to a map/reduce combination in effect:

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .fold(|| 0_u32, |a: u32, b: u8| a + (b as u32))
               .sum::<u32>();

assert_eq!(sum, (0..22).sum()); // compare to sequential

source

fn fold_with<F, T>(self, init: T, fold_op: F) -> FoldWith<Self, T, F>
where F: Fn(T, Self::Item) -> T + Sync + Send, T: Send + Clone,

Applies fold_op to the given init value with each item of this iterator, finally producing the value for further use.

This works essentially like fold(|| init.clone(), fold_op), except it doesn’t require the init type to be Sync, nor any other form of added synchronization.

§Examples

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .fold_with(0_u32, |a: u32, b: u8| a + (b as u32))
               .sum::<u32>();

assert_eq!(sum, (0..22).sum()); // compare to sequential

source

fn try_fold<T, R, ID, F>( self, identity: ID, fold_op: F, ) -> TryFold<Self, R, ID, F>
where F: Fn(T, Self::Item) -> R + Sync + Send, ID: Fn() -> T + Sync + Send, R: Try<Ok = T> + Send,

Performs a fallible parallel fold.

This is a variation of fold() for operations which can fail with Option::None or Result::Err. The first such failure stops processing the local set of items, without affecting other folds in the iterator’s subdivisions.

Often, try_fold() will be followed by try_reduce() for a final reduction and global short-circuiting effect.

§Examples

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .try_fold(|| 0_u32, |a: u32, b: u8| a.checked_add(b as u32))
               .try_reduce(|| 0, u32::checked_add);

assert_eq!(sum, Some((0..22).sum())); // compare to sequential

source

fn try_fold_with<F, T, R>(self, init: T, fold_op: F) -> TryFoldWith<Self, R, F>
where F: Fn(T, Self::Item) -> R + Sync + Send, R: Try<Ok = T> + Send, T: Clone + Send,

Performs a fallible parallel fold with a cloneable init value.

This combines the init semantics of fold_with() and the failure semantics of try_fold().

use rayon::prelude::*;

let bytes = 0..22_u8;
let sum = bytes.into_par_iter()
               .try_fold_with(0_u32, |a: u32, b: u8| a.checked_add(b as u32))
               .try_reduce(|| 0, u32::checked_add);

assert_eq!(sum, Some((0..22).sum())); // compare to sequential

source

fn sum<S>(self) -> S
where S: Send + Sum<Self::Item> + Sum<S>,

Sums up the items in the iterator.

Note that the order in items will be reduced is not specified, so if the + operator is not truly associative (as is the case for floating point numbers), then the results are not fully deterministic.

Basically equivalent to self.reduce(|| 0, |a, b| a + b), except that the type of 0 and the + operation may vary depending on the type of value being produced.

§Examples

use rayon::prelude::*;

let a = [1, 5, 7];

let sum: i32 = a.par_iter().sum();

assert_eq!(sum, 13);

source

fn product(self) -> P
where P: Send + Product<Self::Item> + Product,

Multiplies all the items in the iterator.

Note that the order in items will be reduced is not specified, so if the * operator is not truly associative (as is the case for floating point numbers), then the results are not fully deterministic.

Basically equivalent to self.reduce(|| 1, |a, b| a * b), except that the type of 1 and the * operation may vary depending on the type of value being produced.

§Examples

use rayon::prelude::*;

fn factorial(n: u32) -> u32 {
   (1..n+1).into_par_iter().product()
}

assert_eq!(factorial(0), 1);
assert_eq!(factorial(1), 1);
assert_eq!(factorial(5), 120);

source

fn min(self) -> Option<Self::Item>
where Self::Item: Ord,

Computes the minimum of all the items in the iterator. If the iterator is empty, None is returned; otherwise, Some(min) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

Basically equivalent to self.reduce_with(|a, b| cmp::min(a, b)).

§Examples

use rayon::prelude::*;

let a = [45, 74, 32];

assert_eq!(a.par_iter().min(), Some(&32));

let b: [i32; 0] = [];

assert_eq!(b.par_iter().min(), None);

source

fn min_by<F>(self, f: F) -> Option<Self::Item>
where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,

Computes the minimum of all the items in the iterator with respect to the given comparison function. If the iterator is empty, None is returned; otherwise, Some(min) is returned.

Note that the order in which the items will be reduced is not specified, so if the comparison function is not associative, then the results are not deterministic.

§Examples

use rayon::prelude::*;

let a = [-3_i32, 77, 53, 240, -1];

assert_eq!(a.par_iter().min_by(|x, y| x.cmp(y)), Some(&-3));

source

fn min_by_key<K, F>(self, f: F) -> Option<Self::Item>
where K: Ord + Send, F: Sync + Send + Fn(&Self::Item) -> K,

Computes the item that yields the minimum value for the given function. If the iterator is empty, None is returned; otherwise, Some(item) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

§Examples

use rayon::prelude::*;

let a = [-3_i32, 34, 2, 5, -10, -3, -23];

assert_eq!(a.par_iter().min_by_key(|x| x.abs()), Some(&2));

source

fn max(self) -> Option<Self::Item>
where Self::Item: Ord,

Computes the maximum of all the items in the iterator. If the iterator is empty, None is returned; otherwise, Some(max) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

Basically equivalent to self.reduce_with(|a, b| cmp::max(a, b)).

§Examples

use rayon::prelude::*;

let a = [45, 74, 32];

assert_eq!(a.par_iter().max(), Some(&74));

let b: [i32; 0] = [];

assert_eq!(b.par_iter().max(), None);

source

fn max_by<F>(self, f: F) -> Option<Self::Item>
where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,

Computes the maximum of all the items in the iterator with respect to the given comparison function. If the iterator is empty, None is returned; otherwise, Some(min) is returned.

Note that the order in which the items will be reduced is not specified, so if the comparison function is not associative, then the results are not deterministic.

§Examples

use rayon::prelude::*;

let a = [-3_i32, 77, 53, 240, -1];

assert_eq!(a.par_iter().max_by(|x, y| x.abs().cmp(&y.abs())), Some(&240));

source

fn max_by_key<K, F>(self, f: F) -> Option<Self::Item>
where K: Ord + Send, F: Sync + Send + Fn(&Self::Item) -> K,

Computes the item that yields the maximum value for the given function. If the iterator is empty, None is returned; otherwise, Some(item) is returned.

Note that the order in which the items will be reduced is not specified, so if the Ord impl is not truly associative, then the results are not deterministic.

§Examples

use rayon::prelude::*;

let a = [-3_i32, 34, 2, 5, -10, -3, -23];

assert_eq!(a.par_iter().max_by_key(|x| x.abs()), Some(&34));

source

fn chain<C>(self, chain: C) -> Chain<Self, C::Iter>
where C: IntoParallelIterator<Item = Self::Item>,

Takes two iterators and creates a new iterator over both.

§Examples

use rayon::prelude::*;

let a = [0, 1, 2];
let b = [9, 8, 7];

let par_iter = a.par_iter().chain(b.par_iter());

let chained: Vec<_> = par_iter.cloned().collect();

assert_eq!(&chained[..], &[0, 1, 2, 9, 8, 7]);

source

fn find_any(self, predicate: P) -> Option<Self::Item>
where P: Fn(&Self::Item) -> bool + Sync + Send,

Searches for some item in the parallel iterator that matches the given predicate and returns it. This operation is similar to find on sequential iterators but the item returned may not be the first one in the parallel sequence which matches, since we search the entire sequence in parallel.

Once a match is found, we will attempt to stop processing the rest of the items in the iterator as soon as possible (just as find stops iterating once a match is found).

§Examples

use rayon::prelude::*;

let a = [1, 2, 3, 3];

assert_eq!(a.par_iter().find_any(|&&x| x == 3), Some(&3));

assert_eq!(a.par_iter().find_any(|&&x| x == 100), None);

source

fn find_first(self, predicate: P) -> Option<Self::Item>
where P: Fn(&Self::Item) -> bool + Sync + Send,

Searches for the sequentially first item in the parallel iterator that matches the given predicate and returns it.

Once a match is found, all attempts to the right of the match will be stopped, while attempts to the left must continue in case an earlier match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so “first” may be nebulous. If you just want the first match that discovered anywhere in the iterator, find_any is a better choice.

§Examples

use rayon::prelude::*;

let a = [1, 2, 3, 3];

assert_eq!(a.par_iter().find_first(|&&x| x == 3), Some(&3));

assert_eq!(a.par_iter().find_first(|&&x| x == 100), None);

source

fn find_last(self, predicate: P) -> Option<Self::Item>
where P: Fn(&Self::Item) -> bool + Sync + Send,

Searches for the sequentially last item in the parallel iterator that matches the given predicate and returns it.

Once a match is found, all attempts to the left of the match will be stopped, while attempts to the right must continue in case a later match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so “last” may be nebulous. When the order doesn’t actually matter to you, find_any is a better choice.

§Examples

use rayon::prelude::*;

let a = [1, 2, 3, 3];

assert_eq!(a.par_iter().find_last(|&&x| x == 3), Some(&3));

assert_eq!(a.par_iter().find_last(|&&x| x == 100), None);

source

fn find_map_any<P, R>(self, predicate: P) -> Option<R>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

Applies the given predicate to the items in the parallel iterator and returns any non-None result of the map operation.

Once a non-None value is produced from the map operation, we will attempt to stop processing the rest of the items in the iterator as soon as possible.

Note that this method only returns some item in the parallel iterator that is not None from the map predicate. The item returned may not be the first non-None value produced in the parallel sequence, since the entire sequence is mapped over in parallel.

§Examples

use rayon::prelude::*;

let c = ["lol", "NaN", "5", "5"];

let found_number = c.par_iter().find_map_any(|s| s.parse().ok());

assert_eq!(found_number, Some(5));

source

fn find_map_first<P, R>(self, predicate: P) -> Option<R>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

Applies the given predicate to the items in the parallel iterator and returns the sequentially first non-None result of the map operation.

Once a non-None value is produced from the map operation, all attempts to the right of the match will be stopped, while attempts to the left must continue in case an earlier match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so “first” may be nebulous. If you just want the first non-None value discovered anywhere in the iterator, find_map_any is a better choice.

§Examples

use rayon::prelude::*;

let c = ["lol", "NaN", "2", "5"];

let first_number = c.par_iter().find_map_first(|s| s.parse().ok());

assert_eq!(first_number, Some(2));

source

fn find_map_last<P, R>(self, predicate: P) -> Option<R>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

Applies the given predicate to the items in the parallel iterator and returns the sequentially last non-None result of the map operation.

Once a non-None value is produced from the map operation, all attempts to the left of the match will be stopped, while attempts to the right must continue in case a later match is found.

Note that not all parallel iterators have a useful order, much like sequential HashMap iteration, so “first” may be nebulous. If you just want the first non-None value discovered anywhere in the iterator, find_map_any is a better choice.

§Examples

use rayon::prelude::*;

let c = ["lol", "NaN", "2", "5"];

let last_number = c.par_iter().find_map_last(|s| s.parse().ok());

assert_eq!(last_number, Some(5));

source

fn any(self, predicate: P) -> bool
where P: Fn(Self::Item) -> bool + Sync + Send,

Searches for some item in the parallel iterator that matches the given predicate, and if so returns true. Once a match is found, we’ll attempt to stop process the rest of the items. Proving that there’s no match, returning false, does require visiting every item.

§Examples

use rayon::prelude::*;

let a = [0, 12, 3, 4, 0, 23, 0];

let is_valid = a.par_iter().any(|&x| x > 10);

assert!(is_valid);

source

fn all(self, predicate: P) -> bool
where P: Fn(Self::Item) -> bool + Sync + Send,

Tests that every item in the parallel iterator matches the given predicate, and if so returns true. If a counter-example is found, we’ll attempt to stop processing more items, then return false.

§Examples

use rayon::prelude::*;

let a = [0, 12, 3, 4, 0, 23, 0];

let is_valid = a.par_iter().all(|&x| x > 10);

assert!(!is_valid);

source

fn while_some<T>(self) -> WhileSome<Self>
where Self: ParallelIterator<Item = Option<T>>, T: Send,

Creates an iterator over the Some items of this iterator, halting as soon as any None is found.

§Examples

use rayon::prelude::*;
use std::sync::atomic::{AtomicUsize, Ordering};

let counter = AtomicUsize::new(0);
let value = (0_i32..2048)
    .into_par_iter()
    .map(|x| {
             counter.fetch_add(1, Ordering::SeqCst);
             if x < 1024 { Some(x) } else { None }
         })
    .while_some()
    .max();

assert!(value < Some(1024));
assert!(counter.load(Ordering::SeqCst) < 2048); // should not have visited every single one

source

fn panic_fuse(self) -> PanicFuse<Self>

Wraps an iterator with a fuse in case of panics, to halt all threads as soon as possible.

Panics within parallel iterators are always propagated to the caller, but they don’t always halt the rest of the iterator right away, due to the internal semantics of join. This adaptor makes a greater effort to stop processing other items sooner, with the cost of additional synchronization overhead, which may also inhibit some optimizations.

§Examples

If this code didn’t use panic_fuse(), it would continue processing many more items in other threads (with long sleep delays) before the panic is finally propagated.

use rayon::prelude::*;
use std::{thread, time};

(0..1_000_000)
    .into_par_iter()
    .panic_fuse()
    .for_each(|i| {
        // simulate some work
        thread::sleep(time::Duration::from_secs(1));
        assert!(i > 0); // oops!
    });

source

fn collect<C>(self) -> C
where C: FromParallelIterator<Self::Item>,

Creates a fresh collection containing all the elements produced by this parallel iterator.

You may prefer collect_into_vec() implemented on IndexedParallelIterator, if your underlying iterator also implements it. collect_into_vec() allocates efficiently with precise knowledge of how many elements the iterator contains, and even allows you to reuse an existing vector’s backing store rather than allocating a fresh vector.

§Examples

use rayon::prelude::*;

let sync_vec: Vec<_> = (0..100).into_iter().collect();

let async_vec: Vec<_> = (0..100).into_par_iter().collect();

assert_eq!(sync_vec, async_vec);

You can collect a pair of collections like unzip for paired items:

use rayon::prelude::*;

let a = [(0, 1), (1, 2), (2, 3), (3, 4)];
let (first, second): (Vec<_>, Vec<_>) = a.into_par_iter().collect();

assert_eq!(first, [0, 1, 2, 3]);
assert_eq!(second, [1, 2, 3, 4]);

Or like partition_map for Either items:

use rayon::prelude::*;
use rayon::iter::Either;

let (left, right): (Vec<_>, Vec<_>) = (0..8).into_par_iter().map(|x| {
    if x % 2 == 0 {
        Either::Left(x * 4)
    } else {
        Either::Right(x * 3)
    }
}).collect();

assert_eq!(left, [0, 8, 16, 24]);
assert_eq!(right, [3, 9, 15, 21]);

You can even collect an arbitrarily-nested combination of pairs and Either:

use rayon::prelude::*;
use rayon::iter::Either;

let (first, (left, right)): (Vec<_>, (Vec<_>, Vec<_>))
    = (0..8).into_par_iter().map(|x| {
        if x % 2 == 0 {
            (x, Either::Left(x * 4))
        } else {
            (-x, Either::Right(x * 3))
        }
    }).collect();

assert_eq!(first, [0, -1, 2, -3, 4, -5, 6, -7]);
assert_eq!(left, [0, 8, 16, 24]);
assert_eq!(right, [3, 9, 15, 21]);

All of that can also be combined with short-circuiting collection of Result or Option types:

use rayon::prelude::*;
use rayon::iter::Either;

let result: Result<(Vec<_>, (Vec<_>, Vec<_>)), _>
    = (0..8).into_par_iter().map(|x| {
        if x > 5 {
            Err(x)
        } else if x % 2 == 0 {
            Ok((x, Either::Left(x * 4)))
        } else {
            Ok((-x, Either::Right(x * 3)))
        }
    }).collect();

let error = result.unwrap_err();
assert!(error == 6 || error == 7);

source

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
where Self: ParallelIterator<Item = (A, B)>, FromA: Default + Send + ParallelExtend<A>, FromB: Default + Send + ParallelExtend, A: Send, B: Send,

Unzips the items of a parallel iterator into a pair of arbitrary ParallelExtend containers.

You may prefer to use unzip_into_vecs(), which allocates more efficiently with precise knowledge of how many elements the iterator contains, and even allows you to reuse existing vectors’ backing stores rather than allocating fresh vectors.

§Examples

use rayon::prelude::*;

let a = [(0, 1), (1, 2), (2, 3), (3, 4)];

let (left, right): (Vec<_>, Vec<_>) = a.par_iter().cloned().unzip();

assert_eq!(left, [0, 1, 2, 3]);
assert_eq!(right, [1, 2, 3, 4]);

Nested pairs can be unzipped too.

use rayon::prelude::*;

let (values, (squares, cubes)): (Vec<_>, (Vec<_>, Vec<_>)) = (0..4).into_par_iter()
    .map(|i| (i, (i * i, i * i * i)))
    .unzip();

assert_eq!(values, [0, 1, 2, 3]);
assert_eq!(squares, [0, 1, 4, 9]);
assert_eq!(cubes, [0, 1, 8, 27]);

source

fn partition<A, B, P>(self, predicate: P) -> (A, B)
where A: Default + Send + ParallelExtend<Self::Item>, B: Default + Send + ParallelExtend<Self::Item>, P: Fn(&Self::Item) -> bool + Sync + Send,

Partitions the items of a parallel iterator into a pair of arbitrary ParallelExtend containers. Items for which the predicate returns true go into the first container, and the rest go into the second.

Note: unlike the standard Iterator::partition, this allows distinct collection types for the left and right items. This is more flexible, but may require new type annotations when converting sequential code that used type inferrence assuming the two were the same.

§Examples

use rayon::prelude::*;

let (left, right): (Vec<_>, Vec<_>) = (0..8).into_par_iter().partition(|x| x % 2 == 0);

assert_eq!(left, [0, 2, 4, 6]);
assert_eq!(right, [1, 3, 5, 7]);

source

fn partition_map<A, B, P, L, R>(self, predicate: P) -> (A, B)
where A: Default + Send + ParallelExtend<L>, B: Default + Send + ParallelExtend<R>, P: Fn(Self::Item) -> Either<L, R> + Sync + Send, L: Send, R: Send,

Partitions and maps the items of a parallel iterator into a pair of arbitrary ParallelExtend containers. Either::Left items go into the first container, and Either::Right items go into the second.

§Examples

use rayon::prelude::*;
use rayon::iter::Either;

let (left, right): (Vec<_>, Vec<_>) = (0..8).into_par_iter()
    .partition_map(|x| {
        if x % 2 == 0 {
            Either::Left(x * 4)
        } else {
            Either::Right(x * 3)
        }
    });

assert_eq!(left, [0, 8, 16, 24]);
assert_eq!(right, [3, 9, 15, 21]);

Nested Either enums can be split as well.

use rayon::prelude::*;
use rayon::iter::Either::*;

let ((fizzbuzz, fizz), (buzz, other)): ((Vec<_>, Vec<_>), (Vec<_>, Vec<_>)) = (1..20)
    .into_par_iter()
    .partition_map(|x| match (x % 3, x % 5) {
        (0, 0) => Left(Left(x)),
        (0, _) => Left(Right(x)),
        (_, 0) => Right(Left(x)),
        (_, _) => Right(Right(x)),
    });

assert_eq!(fizzbuzz, [15]);
assert_eq!(fizz, [3, 6, 9, 12, 18]);
assert_eq!(buzz, [5, 10]);
assert_eq!(other, [1, 2, 4, 7, 8, 11, 13, 14, 16, 17, 19]);

source

fn intersperse(self, element: Self::Item) -> Intersperse<Self>
where Self::Item: Clone,

Intersperses clones of an element between items of this iterator.

§Examples

use rayon::prelude::*;

let x = vec![1, 2, 3];
let r: Vec<_> = x.into_par_iter().intersperse(-1).collect();

assert_eq!(r, vec![1, -1, 2, -1, 3]);

source

fn opt_len(&self) -> Option<usize>

Internal method used to define the behavior of this parallel iterator. You should not need to call this directly.

Returns the number of items produced by this iterator, if known statically. This can be used by consumers to trigger special fast paths. Therefore, if Some(_) is returned, this iterator must only use the (indexed) Consumer methods when driving a consumer, such as split_at(). Calling UnindexedConsumer::split_off_left() or other UnindexedConsumer methods – or returning an inaccurate value – may result in panics.

This method is currently used to optimize collect for want of true Rust specialization; it may be removed when specialization is stable.

Object Safety§

This trait is not object safe.

Trait rayon::iter::ParallelIteratorCopy item path

Required Associated Types§

type Item: Send

Required Methods§

fn drive_unindexed<C>(self, consumer: C) -> C::Resultwhere C: UnindexedConsumer<Self::Item>,

Provided Methods§

fn for_each<OP>(self, op: OP)where OP: Fn(Self::Item) + Sync + Send,

§Examples

fn for_each_with<OP, T>(self, init: T, op: OP)where OP: Fn(&mut T, Self::Item) + Sync + Send, T: Send + Clone,

§Examples

fn for_each_init<OP, INIT, T>(self, init: INIT, op: OP)where OP: Fn(&mut T, Self::Item) + Sync + Send, INIT: Fn() -> T + Sync + Send,

§Examples

fn try_for_each<OP, R>(self, op: OP) -> Rwhere OP: Fn(Self::Item) -> R + Sync + Send, R: Try<Ok = ()> + Send,

§Examples

fn try_for_each_with<OP, T, R>(self, init: T, op: OP) -> Rwhere OP: Fn(&mut T, Self::Item) -> R + Sync + Send, T: Send + Clone, R: Try<Ok = ()> + Send,

§Examples

fn try_for_each_init<OP, INIT, T, R>(self, init: INIT, op: OP) -> Rwhere OP: Fn(&mut T, Self::Item) -> R + Sync + Send, INIT: Fn() -> T + Sync + Send, R: Try<Ok = ()> + Send,

§Examples

fn count(self) -> usize

§Examples

fn map<F, R>(self, map_op: F) -> Map<Self, F>where F: Fn(Self::Item) -> R + Sync + Send, R: Send,

§Examples

fn map_with<F, T, R>(self, init: T, map_op: F) -> MapWith<Self, T, F>where F: Fn(&mut T, Self::Item) -> R + Sync + Send, T: Send + Clone, R: Send,

§Examples

fn map_init<F, INIT, T, R>( self, init: INIT, map_op: F, ) -> MapInit<Self, INIT, F>where F: Fn(&mut T, Self::Item) -> R + Sync + Send, INIT: Fn() -> T + Sync + Send, R: Send,

§Examples

fn cloned<'a, T>(self) -> Cloned<Self>where T: 'a + Clone + Send, Self: ParallelIterator<Item = &'a T>,

§Examples

fn copied<'a, T>(self) -> Copied<Self>where T: 'a + Copy + Send, Self: ParallelIterator<Item = &'a T>,

§Examples

fn inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP>where OP: Fn(&Self::Item) + Sync + Send,

§Examples

fn update<F>(self, update_op: F) -> Update<Self, F>where F: Fn(&mut Self::Item) + Sync + Send,

§Examples

fn filter<P>(self, filter_op: P) -> Filter<Self, P>where P: Fn(&Self::Item) -> bool + Sync + Send,

§Examples

fn filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P>where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

§Examples

fn flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F>where F: Fn(Self::Item) -> PI + Sync + Send, PI: IntoParallelIterator,

§Examples

fn flat_map_iter<F, SI>(self, map_op: F) -> FlatMapIter<Self, F>where F: Fn(Self::Item) -> SI + Sync + Send, SI: IntoIterator, SI::Item: Send,

§flat_map_iter versus flat_map

§Examples

fn flatten(self) -> Flatten<Self>where Self::Item: IntoParallelIterator,

§Examples

fn flatten_iter(self) -> FlattenIter<Self>where Self::Item: IntoIterator, <Self::Item as IntoIterator>::Item: Send,

§Examples

fn reduce<OP, ID>(self, identity: ID, op: OP) -> Self::Itemwhere OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send, ID: Fn() -> Self::Item + Sync + Send,

§Examples

fn reduce_with<OP>(self, op: OP) -> Option<Self::Item>where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,

§Examples

fn try_reduce<T, OP, ID>(self, identity: ID, op: OP) -> Self::Itemwhere OP: Fn(T, T) -> Self::Item + Sync + Send, ID: Fn() -> T + Sync + Send, Self::Item: Try<Ok = T>,

§Examples

fn try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item>where OP: Fn(T, T) -> Self::Item + Sync + Send, Self::Item: Try<Ok = T>,

§Examples

fn fold<T, ID, F>(self, identity: ID, fold_op: F) -> Fold<Self, ID, F>where F: Fn(T, Self::Item) -> T + Sync + Send, ID: Fn() -> T + Sync + Send, T: Send,

§Fold versus reduce

§Fold vs Map/Reduce

§Combining fold with other operations

fn fold_with<F, T>(self, init: T, fold_op: F) -> FoldWith<Self, T, F>where F: Fn(T, Self::Item) -> T + Sync + Send, T: Send + Clone,

§Examples

fn try_fold<T, R, ID, F>( self, identity: ID, fold_op: F, ) -> TryFold<Self, R, ID, F>where F: Fn(T, Self::Item) -> R + Sync + Send, ID: Fn() -> T + Sync + Send, R: Try<Ok = T> + Send,

§Examples

fn try_fold_with<F, T, R>(self, init: T, fold_op: F) -> TryFoldWith<Self, R, F>where F: Fn(T, Self::Item) -> R + Sync + Send, R: Try<Ok = T> + Send, T: Clone + Send,

fn sum<S>(self) -> Swhere S: Send + Sum<Self::Item> + Sum<S>,

§Examples

fn product<P>(self) -> Pwhere P: Send + Product<Self::Item> + Product<P>,

§Examples

fn min(self) -> Option<Self::Item>where Self::Item: Ord,

§Examples

fn min_by<F>(self, f: F) -> Option<Self::Item>where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,

§Examples

fn min_by_key<K, F>(self, f: F) -> Option<Self::Item>where K: Ord + Send, F: Sync + Send + Fn(&Self::Item) -> K,

§Examples

fn max(self) -> Option<Self::Item>where Self::Item: Ord,

§Examples

fn max_by<F>(self, f: F) -> Option<Self::Item>where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,

§Examples

fn max_by_key<K, F>(self, f: F) -> Option<Self::Item>where K: Ord + Send, F: Sync + Send + Fn(&Self::Item) -> K,

§Examples

Trait rayon::iter::ParallelIterator

fn drive_unindexed<C>(self, consumer: C) -> C::Result
where C: UnindexedConsumer<Self::Item>,

fn for_each<OP>(self, op: OP)
where OP: Fn(Self::Item) + Sync + Send,

fn for_each_with<OP, T>(self, init: T, op: OP)
where OP: Fn(&mut T, Self::Item) + Sync + Send, T: Send + Clone,

fn for_each_init<OP, INIT, T>(self, init: INIT, op: OP)
where OP: Fn(&mut T, Self::Item) + Sync + Send, INIT: Fn() -> T + Sync + Send,

fn try_for_each<OP, R>(self, op: OP) -> R
where OP: Fn(Self::Item) -> R + Sync + Send, R: Try<Ok = ()> + Send,

fn try_for_each_with<OP, T, R>(self, init: T, op: OP) -> R
where OP: Fn(&mut T, Self::Item) -> R + Sync + Send, T: Send + Clone, R: Try<Ok = ()> + Send,

fn try_for_each_init<OP, INIT, T, R>(self, init: INIT, op: OP) -> R
where OP: Fn(&mut T, Self::Item) -> R + Sync + Send, INIT: Fn() -> T + Sync + Send, R: Try<Ok = ()> + Send,

fn map<F, R>(self, map_op: F) -> Map<Self, F>
where F: Fn(Self::Item) -> R + Sync + Send, R: Send,

fn map_with<F, T, R>(self, init: T, map_op: F) -> MapWith<Self, T, F>
where F: Fn(&mut T, Self::Item) -> R + Sync + Send, T: Send + Clone, R: Send,

fn map_init<F, INIT, T, R>( self, init: INIT, map_op: F, ) -> MapInit<Self, INIT, F>
where F: Fn(&mut T, Self::Item) -> R + Sync + Send, INIT: Fn() -> T + Sync + Send, R: Send,

fn cloned<'a, T>(self) -> Cloned<Self>
where T: 'a + Clone + Send, Self: ParallelIterator<Item = &'a T>,

fn copied<'a, T>(self) -> Copied<Self>
where T: 'a + Copy + Send, Self: ParallelIterator<Item = &'a T>,

fn inspect<OP>(self, inspect_op: OP) -> Inspect<Self, OP>
where OP: Fn(&Self::Item) + Sync + Send,

fn update<F>(self, update_op: F) -> Update<Self, F>
where F: Fn(&mut Self::Item) + Sync + Send,

fn filter<P>(self, filter_op: P) -> Filter<Self, P>
where P: Fn(&Self::Item) -> bool + Sync + Send,

fn filter_map<P, R>(self, filter_op: P) -> FilterMap<Self, P>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

fn flat_map<F, PI>(self, map_op: F) -> FlatMap<Self, F>
where F: Fn(Self::Item) -> PI + Sync + Send, PI: IntoParallelIterator,

fn flat_map_iter<F, SI>(self, map_op: F) -> FlatMapIter<Self, F>
where F: Fn(Self::Item) -> SI + Sync + Send, SI: IntoIterator, SI::Item: Send,

§`flat_map_iter` versus `flat_map`

fn flatten(self) -> Flatten<Self>
where Self::Item: IntoParallelIterator,

fn flatten_iter(self) -> FlattenIter<Self>
where Self::Item: IntoIterator, <Self::Item as IntoIterator>::Item: Send,

fn reduce<OP, ID>(self, identity: ID, op: OP) -> Self::Item
where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send, ID: Fn() -> Self::Item + Sync + Send,

fn reduce_with<OP>(self, op: OP) -> Option<Self::Item>
where OP: Fn(Self::Item, Self::Item) -> Self::Item + Sync + Send,

fn try_reduce<T, OP, ID>(self, identity: ID, op: OP) -> Self::Item
where OP: Fn(T, T) -> Self::Item + Sync + Send, ID: Fn() -> T + Sync + Send, Self::Item: Try<Ok = T>,

fn try_reduce_with<T, OP>(self, op: OP) -> Option<Self::Item>
where OP: Fn(T, T) -> Self::Item + Sync + Send, Self::Item: Try<Ok = T>,

fn fold<T, ID, F>(self, identity: ID, fold_op: F) -> Fold<Self, ID, F>
where F: Fn(T, Self::Item) -> T + Sync + Send, ID: Fn() -> T + Sync + Send, T: Send,

fn fold_with<F, T>(self, init: T, fold_op: F) -> FoldWith<Self, T, F>
where F: Fn(T, Self::Item) -> T + Sync + Send, T: Send + Clone,

fn try_fold<T, R, ID, F>( self, identity: ID, fold_op: F, ) -> TryFold<Self, R, ID, F>
where F: Fn(T, Self::Item) -> R + Sync + Send, ID: Fn() -> T + Sync + Send, R: Try<Ok = T> + Send,

fn try_fold_with<F, T, R>(self, init: T, fold_op: F) -> TryFoldWith<Self, R, F>
where F: Fn(T, Self::Item) -> R + Sync + Send, R: Try<Ok = T> + Send, T: Clone + Send,

fn sum<S>(self) -> S
where S: Send + Sum<Self::Item> + Sum<S>,

fn product<P>(self) -> P
where P: Send + Product<Self::Item> + Product<P>,

fn min(self) -> Option<Self::Item>
where Self::Item: Ord,

fn min_by<F>(self, f: F) -> Option<Self::Item>
where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,

fn min_by_key<K, F>(self, f: F) -> Option<Self::Item>
where K: Ord + Send, F: Sync + Send + Fn(&Self::Item) -> K,

fn max(self) -> Option<Self::Item>
where Self::Item: Ord,

fn max_by<F>(self, f: F) -> Option<Self::Item>
where F: Sync + Send + Fn(&Self::Item, &Self::Item) -> Ordering,

fn max_by_key<K, F>(self, f: F) -> Option<Self::Item>
where K: Ord + Send, F: Sync + Send + Fn(&Self::Item) -> K,

fn chain<C>(self, chain: C) -> Chain<Self, C::Iter>
where C: IntoParallelIterator<Item = Self::Item>,

fn find_any<P>(self, predicate: P) -> Option<Self::Item>
where P: Fn(&Self::Item) -> bool + Sync + Send,

fn find_first<P>(self, predicate: P) -> Option<Self::Item>
where P: Fn(&Self::Item) -> bool + Sync + Send,

fn find_last<P>(self, predicate: P) -> Option<Self::Item>
where P: Fn(&Self::Item) -> bool + Sync + Send,

fn find_map_any<P, R>(self, predicate: P) -> Option<R>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

fn find_map_first<P, R>(self, predicate: P) -> Option<R>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

fn find_map_last<P, R>(self, predicate: P) -> Option<R>
where P: Fn(Self::Item) -> Option<R> + Sync + Send, R: Send,

fn any<P>(self, predicate: P) -> bool
where P: Fn(Self::Item) -> bool + Sync + Send,

fn all<P>(self, predicate: P) -> bool
where P: Fn(Self::Item) -> bool + Sync + Send,

fn while_some<T>(self) -> WhileSome<Self>
where Self: ParallelIterator<Item = Option<T>>, T: Send,

fn collect<C>(self) -> C
where C: FromParallelIterator<Self::Item>,

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
where Self: ParallelIterator<Item = (A, B)>, FromA: Default + Send + ParallelExtend<A>, FromB: Default + Send + ParallelExtend<B>, A: Send, B: Send,

fn partition<A, B, P>(self, predicate: P) -> (A, B)
where A: Default + Send + ParallelExtend<Self::Item>, B: Default + Send + ParallelExtend<Self::Item>, P: Fn(&Self::Item) -> bool + Sync + Send,

fn partition_map<A, B, P, L, R>(self, predicate: P) -> (A, B)
where A: Default + Send + ParallelExtend<L>, B: Default + Send + ParallelExtend<R>, P: Fn(Self::Item) -> Either<L, R> + Sync + Send, L: Send, R: Send,

fn intersperse(self, element: Self::Item) -> Intersperse<Self>
where Self::Item: Clone,

impl<'a, T, I> ParallelIterator for Cloned<I>
where I: ParallelIterator<Item = &'a T>, T: 'a + Clone + Send + Sync,

impl<'a, T, I> ParallelIterator for Copied<I>
where I: ParallelIterator<Item = &'a T>, T: 'a + Copy + Send + Sync,