`pub struct IndexSet<T, S = RandomState> { /* private fields */ }`

## Expand description

A hash set where the iteration order of the values is independent of their hash values.

The interface is closely compatible with the standard `HashSet`

, but also
has additional features.

## Order

The values have a consistent order that is determined by the sequence of insertion and removal calls on the set. The order does not depend on the values or the hash function at all. Note that insertion order and value are not affected if a re-insertion is attempted once an element is already present.

All iterators traverse the set *in order*. Set operation iterators like
`union`

produce a concatenated order, as do their matching “bitwise”
operators. See their documentation for specifics.

The insertion order is preserved, with **notable exceptions** like the
`.remove()`

or `.swap_remove()`

methods. Methods such as `.sort_by()`

of
course result in a new order, depending on the sorting order.

## Indices

The values are indexed in a compact range without holes in the range
`0..self.len()`

. For example, the method `.get_full`

looks up the index for
a value, and the method `.get_index`

looks up the value by index.

## Examples

```
use indexmap::IndexSet;
// Collects which letters appear in a sentence.
let letters: IndexSet<_> = "a short treatise on fungi".chars().collect();
assert!(letters.contains(&'s'));
assert!(letters.contains(&'t'));
assert!(letters.contains(&'u'));
assert!(!letters.contains(&'y'));
```

## Implementations§

source§### impl<T> IndexSet<T>

### impl<T> IndexSet<T>

source#### pub fn with_capacity(n: usize) -> Self

#### pub fn with_capacity(n: usize) -> Self

Create a new set with capacity for `n`

elements.
(Does not allocate if `n`

is zero.)

Computes in **O(n)** time.

source§### impl<T, S> IndexSet<T, S>

### impl<T, S> IndexSet<T, S>

source#### pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self

#### pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self

Create a new set with capacity for `n`

elements.
(Does not allocate if `n`

is zero.)

Computes in **O(n)** time.

source#### pub const fn with_hasher(hash_builder: S) -> Self

#### pub const fn with_hasher(hash_builder: S) -> Self

Create a new set with `hash_builder`

.

This function is `const`

, so it
can be called in `static`

contexts.

source#### pub fn is_empty(&self) -> bool

#### pub fn is_empty(&self) -> bool

Returns true if the set contains no elements.

Computes in **O(1)** time.

source#### pub fn iter(&self) -> Iter<'_, T> ⓘ

#### pub fn iter(&self) -> Iter<'_, T> ⓘ

Return an iterator over the values of the set, in their order

source#### pub fn clear(&mut self)

#### pub fn clear(&mut self)

Remove all elements in the set, while preserving its capacity.

Computes in **O(n)** time.

source#### pub fn truncate(&mut self, len: usize)

#### pub fn truncate(&mut self, len: usize)

Shortens the set, keeping the first `len`

elements and dropping the rest.

If `len`

is greater than the set’s current length, this has no effect.

source#### pub fn drain<R>(&mut self, range: R) -> Drain<'_, T> ⓘwhere

R: RangeBounds<usize>,

#### pub fn drain<R>(&mut self, range: R) -> Drain<'_, T> ⓘwhere

R: RangeBounds<usize>,

Clears the `IndexSet`

in the given index range, returning those values
as a drain iterator.

The range may be any type that implements `RangeBounds<usize>`

,
including all of the `std::ops::Range*`

types, or even a tuple pair of
`Bound`

start and end values. To drain the set entirely, use `RangeFull`

like `set.drain(..)`

.

This shifts down all entries following the drained range to fill the gap, and keeps the allocated memory for reuse.

* Panics* if the starting point is greater than the end point or if
the end point is greater than the length of the set.

source#### pub fn split_off(&mut self, at: usize) -> Selfwhere

S: Clone,

#### pub fn split_off(&mut self, at: usize) -> Selfwhere

S: Clone,

Splits the collection into two at the given index.

Returns a newly allocated set containing the elements in the range
`[at, len)`

. After the call, the original set will be left containing
the elements `[0, at)`

with its previous capacity unchanged.

* Panics* if

`at > len`

.source§### impl<T, S> IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

### impl<T, S> IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

source#### pub fn reserve(&mut self, additional: usize)

#### pub fn reserve(&mut self, additional: usize)

Reserve capacity for `additional`

more values.

Computes in **O(n)** time.

source#### pub fn shrink_to_fit(&mut self)

#### pub fn shrink_to_fit(&mut self)

Shrink the capacity of the set as much as possible.

Computes in **O(n)** time.

source#### pub fn shrink_to(&mut self, min_capacity: usize)

#### pub fn shrink_to(&mut self, min_capacity: usize)

Shrink the capacity of the set with a lower limit.

Computes in **O(n)** time.

source#### pub fn insert(&mut self, value: T) -> bool

#### pub fn insert(&mut self, value: T) -> bool

Insert the value into the set.

If an equivalent item already exists in the set, it returns
`false`

leaving the original value in the set and without
altering its insertion order. Otherwise, it inserts the new
item and returns `true`

.

Computes in **O(1)** time (amortized average).

source#### pub fn insert_full(&mut self, value: T) -> (usize, bool)

#### pub fn insert_full(&mut self, value: T) -> (usize, bool)

Insert the value into the set, and get its index.

If an equivalent item already exists in the set, it returns
the index of the existing item and `false`

, leaving the
original value in the set and without altering its insertion
order. Otherwise, it inserts the new item and returns the index
of the inserted item and `true`

.

Computes in **O(1)** time (amortized average).

source#### pub fn difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Difference<'a, T, S2> ⓘwhere

S2: BuildHasher,

#### pub fn difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Difference<'a, T, S2> ⓘwhere

S2: BuildHasher,

Return an iterator over the values that are in `self`

but not `other`

.

Values are produced in the same order that they appear in `self`

.

source#### pub fn symmetric_difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> SymmetricDifference<'a, T, S, S2> ⓘwhere

S2: BuildHasher,

#### pub fn symmetric_difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> SymmetricDifference<'a, T, S, S2> ⓘwhere

S2: BuildHasher,

Return an iterator over the values that are in `self`

or `other`

,
but not in both.

Values from `self`

are produced in their original order, followed by
values from `other`

in their original order.

source#### pub fn intersection<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Intersection<'a, T, S2> ⓘwhere

S2: BuildHasher,

#### pub fn intersection<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Intersection<'a, T, S2> ⓘwhere

S2: BuildHasher,

Return an iterator over the values that are in both `self`

and `other`

.

Values are produced in the same order that they appear in `self`

.

source#### pub fn union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Union<'a, T, S> ⓘwhere

S2: BuildHasher,

#### pub fn union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Union<'a, T, S> ⓘwhere

S2: BuildHasher,

Return an iterator over all values that are in `self`

or `other`

.

Values from `self`

are produced in their original order, followed by
values that are unique to `other`

in their original order.

source#### pub fn contains<Q>(&self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn contains<Q>(&self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

Return `true`

if an equivalent to `value`

exists in the set.

Computes in **O(1)** time (average).

source#### pub fn get<Q>(&self, value: &Q) -> Option<&T>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn get<Q>(&self, value: &Q) -> Option<&T>where

Q: Hash + Equivalent<T> + ?Sized,

Return a reference to the value stored in the set, if it is present,
else `None`

.

Computes in **O(1)** time (average).

source#### pub fn get_full<Q>(&self, value: &Q) -> Option<(usize, &T)>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn get_full<Q>(&self, value: &Q) -> Option<(usize, &T)>where

Q: Hash + Equivalent<T> + ?Sized,

Return item index and value

source#### pub fn get_index_of<Q>(&self, value: &Q) -> Option<usize>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn get_index_of<Q>(&self, value: &Q) -> Option<usize>where

Q: Hash + Equivalent<T> + ?Sized,

Return item index, if it exists in the set

source#### pub fn replace(&mut self, value: T) -> Option<T>

#### pub fn replace(&mut self, value: T) -> Option<T>

Adds a value to the set, replacing the existing value, if any, that is equal to the given one, without altering its insertion order. Returns the replaced value.

Computes in **O(1)** time (average).

source#### pub fn replace_full(&mut self, value: T) -> (usize, Option<T>)

#### pub fn replace_full(&mut self, value: T) -> (usize, Option<T>)

Adds a value to the set, replacing the existing value, if any, that is equal to the given one, without altering its insertion order. Returns the index of the item and its replaced value.

Computes in **O(1)** time (average).

source#### pub fn remove<Q>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn remove<Q>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

Remove the value from the set, and return `true`

if it was present.

**NOTE:** This is equivalent to `.swap_remove(value)`

, if you want
to preserve the order of the values in the set, use `.shift_remove(value)`

.

Computes in **O(1)** time (average).

source#### pub fn swap_remove<Q>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn swap_remove<Q>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

Remove the value from the set, and return `true`

if it was present.

Like `Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the position of what used to be the last element!**

Return `false`

if `value`

was not in the set.

Computes in **O(1)** time (average).

source#### pub fn shift_remove<Q>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn shift_remove<Q>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T> + ?Sized,

Remove the value from the set, and return `true`

if it was present.

Like `Vec::remove`

, the value is removed by shifting all of the
elements that follow it, preserving their relative order.
**This perturbs the index of all of those elements!**

Return `false`

if `value`

was not in the set.

Computes in **O(n)** time (average).

source#### pub fn take<Q>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn take<Q>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T> + ?Sized,

Removes and returns the value in the set, if any, that is equal to the given one.

**NOTE:** This is equivalent to `.swap_take(value)`

, if you need to
preserve the order of the values in the set, use `.shift_take(value)`

instead.

Computes in **O(1)** time (average).

source#### pub fn swap_take<Q>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn swap_take<Q>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T> + ?Sized,

Removes and returns the value in the set, if any, that is equal to the given one.

Like `Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the position of what used to be the last element!**

Return `None`

if `value`

was not in the set.

Computes in **O(1)** time (average).

source#### pub fn shift_take<Q>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn shift_take<Q>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T> + ?Sized,

Removes and returns the value in the set, if any, that is equal to the given one.

Like `Vec::remove`

, the value is removed by shifting all of the
elements that follow it, preserving their relative order.
**This perturbs the index of all of those elements!**

Return `None`

if `value`

was not in the set.

Computes in **O(n)** time (average).

source#### pub fn swap_remove_full<Q>(&mut self, value: &Q) -> Option<(usize, T)>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn swap_remove_full<Q>(&mut self, value: &Q) -> Option<(usize, T)>where

Q: Hash + Equivalent<T> + ?Sized,

Remove the value from the set return it and the index it had.

Like `Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the position of what used to be the last element!**

Return `None`

if `value`

was not in the set.

source#### pub fn shift_remove_full<Q>(&mut self, value: &Q) -> Option<(usize, T)>where

Q: Hash + Equivalent<T> + ?Sized,

#### pub fn shift_remove_full<Q>(&mut self, value: &Q) -> Option<(usize, T)>where

Q: Hash + Equivalent<T> + ?Sized,

Remove the value from the set return it and the index it had.

Like `Vec::remove`

, the value is removed by shifting all of the
elements that follow it, preserving their relative order.
**This perturbs the index of all of those elements!**

Return `None`

if `value`

was not in the set.

source#### pub fn pop(&mut self) -> Option<T>

#### pub fn pop(&mut self) -> Option<T>

Remove the last value

This preserves the order of the remaining elements.

Computes in **O(1)** time (average).

source#### pub fn retain<F>(&mut self, keep: F)where

F: FnMut(&T) -> bool,

#### pub fn retain<F>(&mut self, keep: F)where

F: FnMut(&T) -> bool,

Scan through each value in the set and keep those where the
closure `keep`

returns `true`

.

The elements are visited in order, and remaining elements keep their order.

Computes in **O(n)** time (average).

source#### pub fn sort(&mut self)where

T: Ord,

#### pub fn sort(&mut self)where

T: Ord,

Sort the set’s values by their default ordering.

See `sort_by`

for details.

source#### pub fn sort_by<F>(&mut self, cmp: F)where

F: FnMut(&T, &T) -> Ordering,

#### pub fn sort_by<F>(&mut self, cmp: F)where

F: FnMut(&T, &T) -> Ordering,

Sort the set’s values in place using the comparison function `cmp`

.

Computes in **O(n log n)** time and **O(n)** space. The sort is stable.

source#### pub fn sorted_by<F>(self, cmp: F) -> IntoIter<T> ⓘwhere

F: FnMut(&T, &T) -> Ordering,

#### pub fn sorted_by<F>(self, cmp: F) -> IntoIter<T> ⓘwhere

F: FnMut(&T, &T) -> Ordering,

Sort the values of the set and return a by-value iterator of the values with the result.

The sort is stable.

source#### pub fn sort_unstable(&mut self)where

T: Ord,

#### pub fn sort_unstable(&mut self)where

T: Ord,

Sort the set’s values by their default ordering.

See `sort_unstable_by`

for details.

source#### pub fn sort_unstable_by<F>(&mut self, cmp: F)where

F: FnMut(&T, &T) -> Ordering,

#### pub fn sort_unstable_by<F>(&mut self, cmp: F)where

F: FnMut(&T, &T) -> Ordering,

Sort the set’s values in place using the comparison funtion `cmp`

.

Computes in **O(n log n)** time. The sort is unstable.

source§### impl<T, S> IndexSet<T, S>

### impl<T, S> IndexSet<T, S>

source#### pub fn get_index(&self, index: usize) -> Option<&T>

#### pub fn get_index(&self, index: usize) -> Option<&T>

Get a value by index

Valid indices are *0 <= index < self.len()*

Computes in **O(1)** time.

source#### pub fn swap_remove_index(&mut self, index: usize) -> Option<T>

#### pub fn swap_remove_index(&mut self, index: usize) -> Option<T>

Remove the value by index

Valid indices are *0 <= index < self.len()*

`Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the position of what used to be the last element!**

Computes in **O(1)** time (average).

source#### pub fn shift_remove_index(&mut self, index: usize) -> Option<T>

#### pub fn shift_remove_index(&mut self, index: usize) -> Option<T>

Remove the value by index

Valid indices are *0 <= index < self.len()*

`Vec::remove`

, the value is removed by shifting all of the
elements that follow it, preserving their relative order.
**This perturbs the index of all of those elements!**

Computes in **O(n)** time (average).

source#### pub fn move_index(&mut self, from: usize, to: usize)

#### pub fn move_index(&mut self, from: usize, to: usize)

Moves the position of a value from one index to another by shifting all other values in-between.

- If
`from < to`

, the other values will shift down while the targeted value moves up. - If
`from > to`

, the other values will shift up while the targeted value moves down.

* Panics* if

`from`

or `to`

are out of bounds.Computes in **O(n)** time (average).

source#### pub fn swap_indices(&mut self, a: usize, b: usize)

#### pub fn swap_indices(&mut self, a: usize, b: usize)

Swaps the position of two values in the set.

* Panics* if

`a`

or `b`

are out of bounds.source§### impl<T, S> IndexSet<T, S>where

T: Eq + Hash,

S: BuildHasher,

### impl<T, S> IndexSet<T, S>where

T: Eq + Hash,

S: BuildHasher,

source#### pub fn is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

#### pub fn is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

Returns `true`

if `self`

has no elements in common with `other`

.

source#### pub fn is_subset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

#### pub fn is_subset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

Returns `true`

if all elements of `self`

are contained in `other`

.

source#### pub fn is_superset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

#### pub fn is_superset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

Returns `true`

if all elements of `other`

are contained in `self`

.

## Trait Implementations§

source§### impl<T, S1, S2> BitAnd<&IndexSet<T, S2>> for &IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

### impl<T, S1, S2> BitAnd<&IndexSet<T, S2>> for &IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

source§### impl<T, S1, S2> BitOr<&IndexSet<T, S2>> for &IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

### impl<T, S1, S2> BitOr<&IndexSet<T, S2>> for &IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

source§### impl<T, S1, S2> BitXor<&IndexSet<T, S2>> for &IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

### impl<T, S1, S2> BitXor<&IndexSet<T, S2>> for &IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

source§### impl<'a, T, S> Extend<&'a T> for IndexSet<T, S>where

T: Hash + Eq + Copy + 'a,

S: BuildHasher,

### impl<'a, T, S> Extend<&'a T> for IndexSet<T, S>where

T: Hash + Eq + Copy + 'a,

S: BuildHasher,

source§#### fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iterable: I)

#### fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iterable: I)

source§#### fn extend_one(&mut self, item: A)

#### fn extend_one(&mut self, item: A)

`extend_one`

)source§#### fn extend_reserve(&mut self, additional: usize)

#### fn extend_reserve(&mut self, additional: usize)

`extend_one`

)source§### impl<T, S> Extend<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

### impl<T, S> Extend<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

source§#### fn extend<I: IntoIterator<Item = T>>(&mut self, iterable: I)

#### fn extend<I: IntoIterator<Item = T>>(&mut self, iterable: I)

source§#### fn extend_one(&mut self, item: A)

#### fn extend_one(&mut self, item: A)

`extend_one`

)source§#### fn extend_reserve(&mut self, additional: usize)

#### fn extend_reserve(&mut self, additional: usize)

`extend_one`

)source§### impl<T, S> FromIterator<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher + Default,

### impl<T, S> FromIterator<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher + Default,

source§#### fn from_iter<I: IntoIterator<Item = T>>(iterable: I) -> Self

#### fn from_iter<I: IntoIterator<Item = T>>(iterable: I) -> Self

source§### impl<T, S> Index<usize> for IndexSet<T, S>

### impl<T, S> Index<usize> for IndexSet<T, S>

Access `IndexSet`

values at indexed positions.

#### Examples

```
use indexmap::IndexSet;
let mut set = IndexSet::new();
for word in "Lorem ipsum dolor sit amet".split_whitespace() {
set.insert(word.to_string());
}
assert_eq!(set[0], "Lorem");
assert_eq!(set[1], "ipsum");
set.reverse();
assert_eq!(set[0], "amet");
assert_eq!(set[1], "sit");
set.sort();
assert_eq!(set[0], "Lorem");
assert_eq!(set[1], "amet");
```

```
use indexmap::IndexSet;
let mut set = IndexSet::new();
set.insert("foo");
println!("{:?}", set[10]); // panics!
```