pub struct Zip<Parts, D> { /* private fields */ }Expand description
Lock step function application across several arrays or other producers.
Zip allows matching several producers to each other elementwise and applying a function over all tuples of elements (one item from each input at a time).
In general, the zip uses a tuple of producers
(NdProducer trait) that all have to be of the
same shape. The NdProducer implementation defines what its item type is
(for example if it’s a shared reference, mutable reference or an array
view etc).
If all the input arrays are of the same memory layout the zip performs much better and the compiler can usually vectorize the loop (if applicable).
The order elements are visited is not specified. The producers don’t have to have the same item type.
The Zip has two methods for function application: for_each and
fold_while. The zip object can be split, which allows parallelization.
A read-only zip object (no mutable producers) can be cloned.
See also the azip!() which offers a convenient shorthand
to common ways to use Zip.
use ndarray::Zip;
use ndarray::Array2;
type M = Array2<f64>;
// Create four 2d arrays of the same size
let mut a = M::zeros((64, 32));
let b = M::from_elem(a.dim(), 1.);
let c = M::from_elem(a.dim(), 2.);
let d = M::from_elem(a.dim(), 3.);
// Example 1: Perform an elementwise arithmetic operation across
// the four arrays a, b, c, d.
Zip::from(&mut a)
.and(&b)
.and(&c)
.and(&d)
.for_each(|w, &x, &y, &z| {
*w += x + y * z;
});
// Example 2: Create a new array `totals` with one entry per row of `a`.
// Use Zip to traverse the rows of `a` and assign to the corresponding
// entry in `totals` with the sum across each row.
// This is possible because the producer for `totals` and the row producer
// for `a` have the same shape and dimensionality.
// The rows producer yields one array view (`row`) per iteration.
use ndarray::{Array1, Axis};
let mut totals = Array1::zeros(a.nrows());
Zip::from(&mut totals)
.and(a.rows())
.for_each(|totals, row| *totals = row.sum());
// Check the result against the built in `.sum_axis()` along axis 1.
assert_eq!(totals, a.sum_axis(Axis(1)));
// Example 3: Recreate Example 2 using map_collect to make a new array
let totals2 = Zip::from(a.rows()).map_collect(|row| row.sum());
// Check the result against the previous example.
assert_eq!(totals, totals2);Source§
Source
Create a new Zip from the input array or other producer p.
The Zip will take the exact dimension of p and all inputs
must have the same dimensions (or be broadcast to them).
Source§
Source
Create a new Zip with an index producer and the producer p.
The Zip will take the exact dimension of p and all inputs
must have the same dimensions (or be broadcast to them).
Note: Indexed zip has overhead.
Source§
Source
Apply a function to all elements of the input arrays, visiting elements in lock step.
Source
Apply a fold function to all elements of the input arrays, visiting elements in lock step.
§Example
The expression tr(AᵀB) can be more efficiently computed as
the equivalent expression ∑ᵢⱼ(A∘B)ᵢⱼ (i.e. the sum of the
elements of the entry-wise product). It would be possible to
evaluate this expression by first computing the entry-wise
product, A∘B, and then computing the elementwise sum of that
product, but it’s possible to do this in a single loop (and
avoid an extra heap allocation if A and B can’t be
consumed) by using Zip:
use ndarray::{array, Zip};
let a = array![[1, 5], [3, 7]];
let b = array![[2, 4], [8, 6]];
// Without using `Zip`. This involves two loops and an extra
// heap allocation for the result of `&a * &b`.
let sum_prod_nonzip = (&a * &b).sum();
// Using `Zip`. This is a single loop without any heap allocations.
let sum_prod_zip = Zip::from(&a).and(&b).fold(0, |acc, a, b| acc + a * b);
assert_eq!(sum_prod_nonzip, sum_prod_zip);Source
Apply a fold function to the input arrays while the return
value is FoldWhile::Continue, visiting elements in lock step.
Source
Tests if every element of the iterator matches a predicate.
Returns true if predicate evaluates to true for all elements.
Returns true if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).all(|&a, &b| a * a == b));Source
Tests if at least one element of the iterator matches a predicate.
Returns true if predicate evaluates to true for at least one element.
Returns false if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).any(|&a, &b| a == b));
assert!(!Zip::from(&a).and(&b).any(|&a, &b| a - 1 == b));Source
Include the producer p in the Zip.
Panics if p’s shape doesn’t match the Zip’s exactly.
Source
Include the producer p in the Zip, broadcasting if needed.
If their shapes disagree, rhs is broadcast to the shape of self.
Panics if broadcasting isn’t possible.
Source
Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source
Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source
Split the Zip evenly in two.
It will be split in the way that best preserves element locality.
Source§
Source
Apply a function to all elements of the input arrays, visiting elements in lock step.
Source
Apply a fold function to all elements of the input arrays, visiting elements in lock step.
§Example
The expression tr(AᵀB) can be more efficiently computed as
the equivalent expression ∑ᵢⱼ(A∘B)ᵢⱼ (i.e. the sum of the
elements of the entry-wise product). It would be possible to
evaluate this expression by first computing the entry-wise
product, A∘B, and then computing the elementwise sum of that
product, but it’s possible to do this in a single loop (and
avoid an extra heap allocation if A and B can’t be
consumed) by using Zip:
use ndarray::{array, Zip};
let a = array![[1, 5], [3, 7]];
let b = array![[2, 4], [8, 6]];
// Without using `Zip`. This involves two loops and an extra
// heap allocation for the result of `&a * &b`.
let sum_prod_nonzip = (&a * &b).sum();
// Using `Zip`. This is a single loop without any heap allocations.
let sum_prod_zip = Zip::from(&a).and(&b).fold(0, |acc, a, b| acc + a * b);
assert_eq!(sum_prod_nonzip, sum_prod_zip);Source
Apply a fold function to the input arrays while the return
value is FoldWhile::Continue, visiting elements in lock step.
Source
Tests if every element of the iterator matches a predicate.
Returns true if predicate evaluates to true for all elements.
Returns true if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).all(|&a, &b| a * a == b));Source
Tests if at least one element of the iterator matches a predicate.
Returns true if predicate evaluates to true for at least one element.
Returns false if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).any(|&a, &b| a == b));
assert!(!Zip::from(&a).and(&b).any(|&a, &b| a - 1 == b));Source
Include the producer p in the Zip.
Panics if p’s shape doesn’t match the Zip’s exactly.
Source
Include the producer p in the Zip, broadcasting if needed.
If their shapes disagree, rhs is broadcast to the shape of self.
Panics if broadcasting isn’t possible.
Source
Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source
Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source
Split the Zip evenly in two.
It will be split in the way that best preserves element locality.
Source§
Source
Apply a function to all elements of the input arrays, visiting elements in lock step.
Source
Apply a fold function to all elements of the input arrays, visiting elements in lock step.
§Example
The expression tr(AᵀB) can be more efficiently computed as
the equivalent expression ∑ᵢⱼ(A∘B)ᵢⱼ (i.e. the sum of the
elements of the entry-wise product). It would be possible to
evaluate this expression by first computing the entry-wise
product, A∘B, and then computing the elementwise sum of that
product, but it’s possible to do this in a single loop (and
avoid an extra heap allocation if A and B can’t be
consumed) by using Zip:
use ndarray::{array, Zip};
let a = array![[1, 5], [3, 7]];
let b = array![[2, 4], [8, 6]];
// Without using `Zip`. This involves two loops and an extra
// heap allocation for the result of `&a * &b`.
let sum_prod_nonzip = (&a * &b).sum();
// Using `Zip`. This is a single loop without any heap allocations.
let sum_prod_zip = Zip::from(&a).and(&b).fold(0, |acc, a, b| acc + a * b);
assert_eq!(sum_prod_nonzip, sum_prod_zip);Source
Apply a fold function to the input arrays while the return
value is FoldWhile::Continue, visiting elements in lock step.
Source
Tests if every element of the iterator matches a predicate.
Returns true if predicate evaluates to true for all elements.
Returns true if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).all(|&a, &b| a * a == b));Source
Tests if at least one element of the iterator matches a predicate.
Returns true if predicate evaluates to true for at least one element.
Returns false if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).any(|&a, &b| a == b));
assert!(!Zip::from(&a).and(&b).any(|&a, &b| a - 1 == b));Source
Include the producer p in the Zip.
Panics if p’s shape doesn’t match the Zip’s exactly.
Source
Include the producer p in the Zip, broadcasting if needed.
If their shapes disagree, rhs is broadcast to the shape of self.
Panics if broadcasting isn’t possible.
Source
Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source
Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source
Split the Zip evenly in two.
It will be split in the way that best preserves element locality.
Source§
Source
Apply a function to all elements of the input arrays, visiting elements in lock step.
Source
Apply a fold function to all elements of the input arrays, visiting elements in lock step.
§Example
The expression tr(AᵀB) can be more efficiently computed as
the equivalent expression ∑ᵢⱼ(A∘B)ᵢⱼ (i.e. the sum of the
elements of the entry-wise product). It would be possible to
evaluate this expression by first computing the entry-wise
product, A∘B, and then computing the elementwise sum of that
product, but it’s possible to do this in a single loop (and
avoid an extra heap allocation if A and B can’t be
consumed) by using Zip:
use ndarray::{array, Zip};
let a = array![[1, 5], [3, 7]];
let b = array![[2, 4], [8, 6]];
// Without using `Zip`. This involves two loops and an extra
// heap allocation for the result of `&a * &b`.
let sum_prod_nonzip = (&a * &b).sum();
// Using `Zip`. This is a single loop without any heap allocations.
let sum_prod_zip = Zip::from(&a).and(&b).fold(0, |acc, a, b| acc + a * b);
assert_eq!(sum_prod_nonzip, sum_prod_zip);Source
Apply a fold function to the input arrays while the return
value is FoldWhile::Continue, visiting elements in lock step.
Source
Tests if every element of the iterator matches a predicate.
Returns true if predicate evaluates to true for all elements.
Returns true if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).all(|&a, &b| a * a == b));Source
Tests if at least one element of the iterator matches a predicate.
Returns true if predicate evaluates to true for at least one element.
Returns false if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).any(|&a, &b| a == b));
assert!(!Zip::from(&a).and(&b).any(|&a, &b| a - 1 == b));Source
Include the producer p in the Zip.
Panics if p’s shape doesn’t match the Zip’s exactly.
Source
Include the producer p in the Zip, broadcasting if needed.
If their shapes disagree, rhs is broadcast to the shape of self.
Panics if broadcasting isn’t possible.
Source
Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source
Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source
Split the Zip evenly in two.
It will be split in the way that best preserves element locality.
Source§
Source
Apply a function to all elements of the input arrays, visiting elements in lock step.
Source
Apply a fold function to all elements of the input arrays, visiting elements in lock step.
§Example
The expression tr(AᵀB) can be more efficiently computed as
the equivalent expression ∑ᵢⱼ(A∘B)ᵢⱼ (i.e. the sum of the
elements of the entry-wise product). It would be possible to
evaluate this expression by first computing the entry-wise
product, A∘B, and then computing the elementwise sum of that
product, but it’s possible to do this in a single loop (and
avoid an extra heap allocation if A and B can’t be
consumed) by using Zip:
use ndarray::{array, Zip};
let a = array![[1, 5], [3, 7]];
let b = array![[2, 4], [8, 6]];
// Without using `Zip`. This involves two loops and an extra
// heap allocation for the result of `&a * &b`.
let sum_prod_nonzip = (&a * &b).sum();
// Using `Zip`. This is a single loop without any heap allocations.
let sum_prod_zip = Zip::from(&a).and(&b).fold(0, |acc, a, b| acc + a * b);
assert_eq!(sum_prod_nonzip, sum_prod_zip);Source
Apply a fold function to the input arrays while the return
value is FoldWhile::Continue, visiting elements in lock step.
Source
Tests if every element of the iterator matches a predicate.
Returns true if predicate evaluates to true for all elements.
Returns true if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).all(|&a, &b| a * a == b));Source
Tests if at least one element of the iterator matches a predicate.
Returns true if predicate evaluates to true for at least one element.
Returns false if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).any(|&a, &b| a == b));
assert!(!Zip::from(&a).and(&b).any(|&a, &b| a - 1 == b));Source
Include the producer p in the Zip.
Panics if p’s shape doesn’t match the Zip’s exactly.
Source
Include the producer p in the Zip, broadcasting if needed.
If their shapes disagree, rhs is broadcast to the shape of self.
Panics if broadcasting isn’t possible.
Source
Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source
Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source
Split the Zip evenly in two.
It will be split in the way that best preserves element locality.
Source§
Source
Apply a function to all elements of the input arrays, visiting elements in lock step.
Source
Apply a fold function to all elements of the input arrays, visiting elements in lock step.
§Example
The expression tr(AᵀB) can be more efficiently computed as
the equivalent expression ∑ᵢⱼ(A∘B)ᵢⱼ (i.e. the sum of the
elements of the entry-wise product). It would be possible to
evaluate this expression by first computing the entry-wise
product, A∘B, and then computing the elementwise sum of that
product, but it’s possible to do this in a single loop (and
avoid an extra heap allocation if A and B can’t be
consumed) by using Zip:
use ndarray::{array, Zip};
let a = array![[1, 5], [3, 7]];
let b = array![[2, 4], [8, 6]];
// Without using `Zip`. This involves two loops and an extra
// heap allocation for the result of `&a * &b`.
let sum_prod_nonzip = (&a * &b).sum();
// Using `Zip`. This is a single loop without any heap allocations.
let sum_prod_zip = Zip::from(&a).and(&b).fold(0, |acc, a, b| acc + a * b);
assert_eq!(sum_prod_nonzip, sum_prod_zip);Source
Apply a fold function to the input arrays while the return
value is FoldWhile::Continue, visiting elements in lock step.
Source
Tests if every element of the iterator matches a predicate.
Returns true if predicate evaluates to true for all elements.
Returns true if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).all(|&a, &b| a * a == b));Source
Tests if at least one element of the iterator matches a predicate.
Returns true if predicate evaluates to true for at least one element.
Returns false if the input arrays are empty.
Example:
use ndarray::{array, Zip};
let a = array![1, 2, 3];
let b = array![1, 4, 9];
assert!(Zip::from(&a).and(&b).any(|&a, &b| a == b));
assert!(!Zip::from(&a).and(&b).any(|&a, &b| a - 1 == b));Source
Split the Zip evenly in two.
It will be split in the way that best preserves element locality.
Source§
Source Available on crate feature rayon only.
rayon only.The par_for_each method for Zip.
This is a shorthand for using .into_par_iter().for_each() on
Zip.
Requires crate feature rayon.
Source Available on crate feature rayon only.
rayon only.Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source Available on crate feature rayon only.
rayon only.Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source Available on crate feature rayon only.
rayon only.Parallel version of fold.
Splits the producer in multiple tasks which each accumulate a single value
using the fold closure. Those tasks are executed in parallel and their results
are then combined to a single value using the reduce closure.
The identity closure provides the initial values for each of the tasks and
for the final reduction.
This is a shorthand for calling self.into_par_iter().fold(...).reduce(...).
Note that it is often more efficient to parallelize not per-element but rather based on larger chunks of an array like generalized rows and operating on each chunk using a sequential variant of the accumulation. For example, sum each row sequentially and in parallel, taking advantage of locality and vectorization within each task, and then reduce their sums to the sum of the matrix.
Also note that the splitting of the producer into multiple tasks is not deterministic which needs to be considered when the accuracy of such an operation is analyzed.
§Examples
use ndarray::{Array, Zip};
let a = Array::<usize, _>::ones((128, 1024));
let b = Array::<usize, _>::ones(128);
let weighted_sum = Zip::from(a.rows()).and(&b).par_fold(
|| 0,
|sum, row, factor| sum + row.sum() * factor,
|sum, other_sum| sum + other_sum,
);
assert_eq!(weighted_sum, a.len());Source§
Source Available on crate feature rayon only.
rayon only.The par_for_each method for Zip.
This is a shorthand for using .into_par_iter().for_each() on
Zip.
Requires crate feature rayon.
Source Available on crate feature rayon only.
rayon only.Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source Available on crate feature rayon only.
rayon only.Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source Available on crate feature rayon only.
rayon only.Parallel version of fold.
Splits the producer in multiple tasks which each accumulate a single value
using the fold closure. Those tasks are executed in parallel and their results
are then combined to a single value using the reduce closure.
The identity closure provides the initial values for each of the tasks and
for the final reduction.
This is a shorthand for calling self.into_par_iter().fold(...).reduce(...).
Note that it is often more efficient to parallelize not per-element but rather based on larger chunks of an array like generalized rows and operating on each chunk using a sequential variant of the accumulation. For example, sum each row sequentially and in parallel, taking advantage of locality and vectorization within each task, and then reduce their sums to the sum of the matrix.
Also note that the splitting of the producer into multiple tasks is not deterministic which needs to be considered when the accuracy of such an operation is analyzed.
§Examples
use ndarray::{Array, Zip};
let a = Array::<usize, _>::ones((128, 1024));
let b = Array::<usize, _>::ones(128);
let weighted_sum = Zip::from(a.rows()).and(&b).par_fold(
|| 0,
|sum, row, factor| sum + row.sum() * factor,
|sum, other_sum| sum + other_sum,
);
assert_eq!(weighted_sum, a.len());Source§
Source Available on crate feature rayon only.
rayon only.The par_for_each method for Zip.
This is a shorthand for using .into_par_iter().for_each() on
Zip.
Requires crate feature rayon.
Source Available on crate feature rayon only.
rayon only.Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source Available on crate feature rayon only.
rayon only.Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source Available on crate feature rayon only.
rayon only.Parallel version of fold.
Splits the producer in multiple tasks which each accumulate a single value
using the fold closure. Those tasks are executed in parallel and their results
are then combined to a single value using the reduce closure.
The identity closure provides the initial values for each of the tasks and
for the final reduction.
This is a shorthand for calling self.into_par_iter().fold(...).reduce(...).
Note that it is often more efficient to parallelize not per-element but rather based on larger chunks of an array like generalized rows and operating on each chunk using a sequential variant of the accumulation. For example, sum each row sequentially and in parallel, taking advantage of locality and vectorization within each task, and then reduce their sums to the sum of the matrix.
Also note that the splitting of the producer into multiple tasks is not deterministic which needs to be considered when the accuracy of such an operation is analyzed.
§Examples
use ndarray::{Array, Zip};
let a = Array::<usize, _>::ones((128, 1024));
let b = Array::<usize, _>::ones(128);
let weighted_sum = Zip::from(a.rows()).and(&b).par_fold(
|| 0,
|sum, row, factor| sum + row.sum() * factor,
|sum, other_sum| sum + other_sum,
);
assert_eq!(weighted_sum, a.len());Source§
Source Available on crate feature rayon only.
rayon only.The par_for_each method for Zip.
This is a shorthand for using .into_par_iter().for_each() on
Zip.
Requires crate feature rayon.
Source Available on crate feature rayon only.
rayon only.Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source Available on crate feature rayon only.
rayon only.Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source Available on crate feature rayon only.
rayon only.Parallel version of fold.
Splits the producer in multiple tasks which each accumulate a single value
using the fold closure. Those tasks are executed in parallel and their results
are then combined to a single value using the reduce closure.
The identity closure provides the initial values for each of the tasks and
for the final reduction.
This is a shorthand for calling self.into_par_iter().fold(...).reduce(...).
Note that it is often more efficient to parallelize not per-element but rather based on larger chunks of an array like generalized rows and operating on each chunk using a sequential variant of the accumulation. For example, sum each row sequentially and in parallel, taking advantage of locality and vectorization within each task, and then reduce their sums to the sum of the matrix.
Also note that the splitting of the producer into multiple tasks is not deterministic which needs to be considered when the accuracy of such an operation is analyzed.
§Examples
use ndarray::{Array, Zip};
let a = Array::<usize, _>::ones((128, 1024));
let b = Array::<usize, _>::ones(128);
let weighted_sum = Zip::from(a.rows()).and(&b).par_fold(
|| 0,
|sum, row, factor| sum + row.sum() * factor,
|sum, other_sum| sum + other_sum,
);
assert_eq!(weighted_sum, a.len());Source§
Source Available on crate feature rayon only.
rayon only.The par_for_each method for Zip.
This is a shorthand for using .into_par_iter().for_each() on
Zip.
Requires crate feature rayon.
Source Available on crate feature rayon only.
rayon only.Map and collect the results into a new array, which has the same size as the inputs.
If all inputs are c- or f-order respectively, that is preserved in the output.
Source Available on crate feature rayon only.
rayon only.Map and assign the results into the producer into, which should have the same
size as the other inputs.
The producer should have assignable items as dictated by the AssignElem trait,
for example &mut R.
Source Available on crate feature rayon only.
rayon only.Parallel version of fold.
Splits the producer in multiple tasks which each accumulate a single value
using the fold closure. Those tasks are executed in parallel and their results
are then combined to a single value using the reduce closure.
The identity closure provides the initial values for each of the tasks and
for the final reduction.
This is a shorthand for calling self.into_par_iter().fold(...).reduce(...).
Note that it is often more efficient to parallelize not per-element but rather based on larger chunks of an array like generalized rows and operating on each chunk using a sequential variant of the accumulation. For example, sum each row sequentially and in parallel, taking advantage of locality and vectorization within each task, and then reduce their sums to the sum of the matrix.
Also note that the splitting of the producer into multiple tasks is not deterministic which needs to be considered when the accuracy of such an operation is analyzed.
§Examples
use ndarray::{Array, Zip};
let a = Array::<usize, _>::ones((128, 1024));
let b = Array::<usize, _>::ones(128);
let weighted_sum = Zip::from(a.rows()).and(&b).par_fold(
|| 0,
|sum, row, factor| sum + row.sum() * factor,
|sum, other_sum| sum + other_sum,
);
assert_eq!(weighted_sum, a.len());