pub trait Reduce<G: Scope, K: Data, V: Data, R: Semigroup>{
// Required method
fn reduce_named<L, V2: Data, R2: Ord + Abelian + 'static>(
&self,
name: &str,
logic: L,
) -> Collection<G, (K, V2), R2>
where L: FnMut(&K, &[(&V, R)], &mut Vec<(V2, R2)>) + 'static;
// Provided method
fn reduce<L, V2: Data, R2: Ord + Abelian + 'static>(
&self,
logic: L,
) -> Collection<G, (K, V2), R2>
where L: FnMut(&K, &[(&V, R)], &mut Vec<(V2, R2)>) + 'static { ... }
}
Expand description
Extension trait for the reduce
differential dataflow method.
Required Methods§
Provided Methods§
Sourcefn reduce<L, V2: Data, R2: Ord + Abelian + 'static>(
&self,
logic: L,
) -> Collection<G, (K, V2), R2>
fn reduce<L, V2: Data, R2: Ord + Abelian + 'static>( &self, logic: L, ) -> Collection<G, (K, V2), R2>
Applies a reduction function on records grouped by key.
Input data must be structured as (key, val)
pairs.
The user-supplied reduction function takes as arguments
- a reference to the key,
- a reference to the slice of values and their accumulated updates,
- a mutuable reference to a vector to populate with output values and accumulated updates.
The user logic is only invoked for non-empty input collections, and it is safe to assume that the
slice of input values is non-empty. The values are presented in sorted order, as defined by their
Ord
implementations.
§Examples
use differential_dataflow::input::Input;
use differential_dataflow::operators::Reduce;
::timely::example(|scope| {
// report the smallest value for each group
scope.new_collection_from(1 .. 10).1
.map(|x| (x / 3, x))
.reduce(|_key, input, output| {
output.push((*input[0].0, 1))
});
});
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.