https://github.com/stdlib-js/strided-base-map-by2

Apply a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assign results to a strided output array.
https://github.com/stdlib-js/strided-base-map-by2

accessor apply array base binary callback clbk foreach javascript map ndarray node node-js nodejs stdlib strided transform

Last synced: 8 months ago
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Apply a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assign results to a strided output array.

Host: GitHub
URL: https://github.com/stdlib-js/strided-base-map-by2
Owner: stdlib-js
License: apache-2.0
Created: 2021-10-28T08:56:53.000Z (about 4 years ago)
Default Branch: main
Last Pushed: 2025-03-17T07:53:20.000Z (9 months ago)
Last Synced: 2025-04-11T18:30:52.821Z (9 months ago)
Topics: accessor, apply, array, base, binary, callback, clbk, foreach, javascript, map, ndarray, node, node-js, nodejs, stdlib, strided, transform
Language: JavaScript
Homepage: https://github.com/stdlib-js/stdlib
Size: 1.17 MB
Stars: 2
Watchers: 3
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md

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# mapBy2

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] 

> Apply a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assign results to a strided output array.

## Installation

```bash

npm install @stdlib/strided-base-map-by2

```

Alternatively,

-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).

The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

## Usage

```javascript

var mapBy2 = require( '@stdlib/strided-base-map-by2' );

```

#### mapBy2( N, x, strideX, y, strideY, z, strideZ, fcn, clbk\[, thisArg] )

Applies a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assigns results to a strided output array.

```javascript

var add = require( '@stdlib/number-float64-base-add' );

function accessor( values ) {

    values[ 0 ] *= 2.0;

    values[ 1 ] *= 2.0;

    return values;

}

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0, 4.0, 4.0 ];

var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2( x.length, x, 1, y, 1, z, 1, add, accessor );

// z => [ -2.0, 4.0, 10.0, -6.0, 14.0, 6.0, 6.0, 2.0 ]

```

The function accepts the following arguments:

-   **N**: number of indexed elements.

-   **x**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions).

-   **strideX**: index increment for `x`.

-   **y**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions).

-   **strideY**: index increment for `y`.

-   **z**: output [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions).

-   **strideZ**: index increment for `z`.

-   **fcn**: binary function to apply to callback return values.

-   **clbk**: callback function which returns an array-like object containing two values.

-   **thisArg**: execution context (_optional_).

The invoked callback function is provided four arguments:

-   **values**: input array element values `[vx, vy]`.

-   **idx**: iteration index (zero-based).

-   **indices**: input and output array strided indices `[ix, iy, iz]` (computed according to `offset + idx*stride`).

-   **arrays**: input and output arrays/collections `[x, y, z]`.

To set the callback execution context, provide a `thisArg`.

```javascript

var add = require( '@stdlib/number-float64-base-add' );

function accessor( values ) {

    this.count += 1;

    values[ 0 ] *= 2.0;

    values[ 1 ] *= 2.0;

    return values;

}

var context = {

    'count': 0

};

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0, 4.0, 4.0 ];

var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2( x.length, x, 1, y, 1, z, 1, add, accessor, context );

// z => [ -2.0, 4.0, 10.0, -6.0, 14.0, 6.0, 6.0, 2.0 ]

var cnt = context.count;

// returns 8

```

The `N` and `stride` parameters determine which elements in the strided arrays are accessed at runtime. For example, to index every other value in `x` and to index the first `N` elements of `y` in reverse order,

```javascript

var add = require( '@stdlib/number-float64-base-add' );

function accessor( values ) {

    values[ 0 ] *= 2.0;

    values[ 1 ] *= 2.0;

    return values;

}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ];

var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0 ];

var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2( 3, x, 2, y, -1, z, 1, add, accessor );

// z => [ 2.0, -4.0, -8.0, 0.0, 0.0, 0.0 ]

```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

```javascript

var Float64Array = require( '@stdlib/array-float64' );

var add = require( '@stdlib/number-float64-base-add' );

function accessor( values ) {

    values[ 0 ] *= 2.0;

    values[ 1 ] *= 2.0;

    return values;

}

// Initial arrays...

var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );

var y0 = new Float64Array( [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0 ] );

var z0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...

var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

var z1 = new Float64Array( z0.buffer, z0.BYTES_PER_ELEMENT*2 ); // start at 3rd element

mapBy2( 3, x1, -2, y1, 1, z1, 1, add, accessor );

// z0 => [ 0.0, 0.0, -8.0, -2.0, 2.0, 0.0 ]

```

#### mapBy2.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, z, strideZ, offsetZ, fcn, clbk\[, thisArg] )

Applies a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assigns results to a strided output array using alternative indexing semantics.

```javascript

var add = require( '@stdlib/number-float64-base-add' );

function accessor( values ) {

    values[ 0 ] *= 2.0;

    values[ 1 ] *= 2.0;

    return values;

}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0 ];

var y = [ 1.0, 1.0, 2.0, 2.0, 3.0 ];

var z = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2.ndarray( x.length, x, 1, 0, y, 1, 0, z, 1, 0, add, accessor );

// z => [ 0.0, -2.0, -2.0, -4.0, -4.0 ]

```

The function accepts the following additional arguments:

-   **offsetX**: starting index for `x`.

-   **offsetY**: starting index for `y`.

-   **offsetZ**: starting index for `z`.

While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the offset parameters support indexing semantics based on starting indices. For example, to index every other value in `x` starting from the second value and to index the last `N` elements in `y` in reverse order,

```javascript

var add = require( '@stdlib/number-float64-base-add' );

function accessor( values ) {

    values[ 0 ] *= 2.0;

    values[ 1 ] *= 2.0;

    return values;

}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ];

var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0 ];

var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2.ndarray( 3, x, 2, 1, y, -1, y.length-1, z, 1, 3, add, accessor );

// z => [ 0.0, 0.0, 0.0, 2.0, -2.0, -8.0 ]

```

## Notes

-   If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**.

    ```javascript

    var add = require( '@stdlib/number-float64-base-add' );

    function accessor() {

        // No-op...

    }

    var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

    var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0, 4.0, 4.0 ];

    var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

    mapBy2( x.length, x, 1, y, 1, z, 1, add, accessor );

    // z => [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]

    ```

## Examples

```javascript

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;

var filledarray = require( '@stdlib/array-filled' );

var filledarrayBy = require( '@stdlib/array-filled-by' );

var add = require( '@stdlib/number-float64-base-add' );

var mapBy2 = require( '@stdlib/strided-base-map-by2' );

function accessor( values, i ) {

    if ( (i%3) === 0 ) {

        // Simulate a "missing" value...

        return;

    }

    return values;

}

var x = filledarrayBy( 10, 'generic', discreteUniform( -100, 100 ) );

console.log( x );

var y = filledarrayBy( 10, 'generic', discreteUniform( -100, 100 ) );

console.log( y );

var z = filledarray( null, 10, 'generic' );

console.log( z );

mapBy2.ndarray( x.length, x, 1, 0, y, -1, y.length-1, z, 1, 0, add, accessor );

console.log( z );

```

* * *

## See Also

-   [`@stdlib/strided-base/map-by`][@stdlib/strided/base/map-by]: apply a unary function to each element retrieved from a strided input array according to a callback function and assign results to a strided output array.

-   [`@stdlib/strided-base/binary`][@stdlib/strided/base/binary]: apply a binary callback to elements in strided input arrays and assign results to elements in a strided output array.

* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].

## Copyright

Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].

[npm-image]: http://img.shields.io/npm/v/@stdlib/strided-base-map-by2.svg

[npm-url]: https://npmjs.org/package/@stdlib/strided-base-map-by2

[test-image]: https://github.com/stdlib-js/strided-base-map-by2/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/strided-base-map-by2/actions/workflows/test.yml?query=branch:main

[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/strided-base-map-by2/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/strided-base-map-by2?branch=main

[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im

[stdlib]: https://github.com/stdlib-js/stdlib

[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors

[umd]: https://github.com/umdjs/umd

[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/strided-base-map-by2/tree/deno

[deno-readme]: https://github.com/stdlib-js/strided-base-map-by2/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/strided-base-map-by2/tree/umd

[umd-readme]: https://github.com/stdlib-js/strided-base-map-by2/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/strided-base-map-by2/tree/esm

[esm-readme]: https://github.com/stdlib-js/strided-base-map-by2/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/strided-base-map-by2/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/strided-base-map-by2/main/LICENSE

[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

[@stdlib/strided/base/map-by]: https://github.com/stdlib-js/strided-base-map-by

[@stdlib/strided/base/binary]: https://github.com/stdlib-js/strided-base-binary

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