@stdlib/utils-map

Apply a function to each element in an array and assign the result to an element in an output array.

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Keywords

array call element-wise elementwise invoke javascript map matrix ndarray node node-js nodejs stdlib tensor transform util utilities utility utils vector

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Apply a function to each element in an array and assign the result to an element in an output array.

Basic Info

Host: GitHub
Owner: stdlib-js
License: apache-2.0
Language: JavaScript
Default Branch: main
Homepage: https://github.com/stdlib-js/stdlib
Size: 2.04 MB

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array call element-wise elementwise invoke javascript map matrix ndarray node node-js nodejs stdlib tensor transform util utilities utility utils vector

Created about 4 years ago · Last pushed 7 months ago

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Readme Changelog Contributing License Code of conduct Citation Security

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

map

Apply a function to each element in an array and assign the result to an element in an output array.

## Installation ```bash npm install @stdlib/utils-map ``` 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 map = require( '@stdlib/utils-map' ); ``` #### map( arr, fcn\[, thisArg] ) Applies a function to each element in an array and assigns the result to an element in a new array. ```javascript var naryFunction = require( '@stdlib/utils-nary-function' ); var abs = require( '@stdlib/math-base-special-abs' ); var arr = [ -1, -2, -3, -4, -5, -6 ]; var out = map( arr, naryFunction( abs, 1 ) ); // returns [ 1, 2, 3, 4, 5, 6 ] ``` The function accepts both array-like objects and [`ndarray`][@stdlib/ndarray/ctor]-like objects. ```javascript var naryFunction = require( '@stdlib/utils-nary-function' ); var abs = require( '@stdlib/math-base-special-abs' ); var array = require( '@stdlib/ndarray-array' ); var opts = { 'dtype': 'generic' }; var arr = array( [ [ -1, -2, -3 ], [ -4, -5, -6 ] ], opts ); var out = map( arr, naryFunction( abs, 1 ) ); // returns var v = out.get( 1, 1 ); // returns 5 ``` The applied function is provided the following arguments: - **value**: array element. - **index**: element index. - **arr**: input array. To set the `this` context when invoking the input function, provide a `thisArg`. ```javascript var abs = require( '@stdlib/math-base-special-abs' ); function fcn( v ) { this.count += 1; return abs( v ); } var arr = [ -1, -2, -3, -4, -5, -6 ]; var ctx = { 'count': 0 }; var out = map( arr, fcn, ctx ); // returns [ 1, 2, 3, 4, 5, 6 ] var cnt = ctx.count; // returns 6 ``` #### map.assign( arr, out, fcn\[, thisArg] ) Applies a function to each element in an array and assigns the result to an element in an output array. ```javascript var naryFunction = require( '@stdlib/utils-nary-function' ); var abs = require( '@stdlib/math-base-special-abs' ); var arr = [ -1, -2, -3, -4, -5, -6 ]; var out = [ 0, 0, 0, 0, 0, 0 ]; map.assign( arr, out, naryFunction( abs, 1 ) ); console.log( out ); // => [ 1, 2, 3, 4, 5, 6 ] ``` The method accepts both array-like objects and [`ndarray`][@stdlib/ndarray/ctor]-like objects. ```javascript var naryFunction = require( '@stdlib/utils-nary-function' ); var abs = require( '@stdlib/math-base-special-abs' ); var array = require( '@stdlib/ndarray-array' ); var opts = { 'dtype': 'generic', 'shape': [ 2, 3 ] }; var arr = array( [ [ -1, -2, -3 ], [ -4, -5, -6 ] ], opts ); var out = array( opts ); map.assign( arr, out, naryFunction( abs, 1 ) ); var v = out.get( 1, 1 ); // returns 5 ``` Input and output arrays must be either both array-like objects or both [`ndarray`][@stdlib/ndarray/ctor]-like objects. If input and output arrays are both array-like objects, both arrays **must** have the same number of elements. If input and output arrays are both [`ndarray`][@stdlib/ndarray/ctor]-like objects, the arrays **must** be [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes]. To map from an input [`ndarray`][@stdlib/ndarray/ctor] to an output [`ndarray`][@stdlib/ndarray/ctor] which has the same rank (i.e., dimensionality) and the same number of elements, but which is not [broadcast compatible][@stdlib/ndarray/base/broadcast-shapes], reshape the arrays prior to invocation. ```javascript var naryFunction = require( '@stdlib/utils-nary-function' ); var abs = require( '@stdlib/math-base-special-abs' ); var array = require( '@stdlib/ndarray-array' ); var opts = { 'dtype': 'generic', 'shape': [ 2, 3 ] }; var arr = array( [ [ -1, -2, -3 ], [ -4, -5, -6 ] ], opts ); opts = { 'dtype': 'generic', 'shape': [ 2, 2, 3 ] // broadcast compatible shape }; var out = array( opts ); map.assign( arr, out, naryFunction( abs, 1 ) ); var v = out.get( 0, 1, 1 ); // returns 5 v = out.get( 1, 1, 1 ); // returns 5 ``` In general, avoid providing output [`ndarray`][@stdlib/ndarray/ctor]-like objects which are [non-contiguous][@stdlib/ndarray/base/assert/is-contiguous] views containing one or more elements referring to the **same** memory location. Writing to an overlapping [non-contiguous][@stdlib/ndarray/base/assert/is-contiguous] view is likely to simultaneously affect multiple elements and yield unexpected results. The applied function is provided the same arguments as with [`map`](#fcn-map).

## Notes - The [`map`](#fcn-map) function **always** returns an output value having a "generic" data type. For example, if provided an array-like object, the function returns a generic `array`. If provided an [`ndarray`][@stdlib/ndarray/ctor], the function returns an [`ndarray`][@stdlib/ndarray/ctor] having a "generic" data type. Accordingly, in contrast to [`TypedArray.prototype.map()`][mdn-typedarray-map], when provided a typed array, the [`map`](#fcn-map) function does **not** return a typed array of the same type. To assign results to a typed array, use the [`map.assign`](#method-map-assign) method. - Both [`map`](#fcn-map) and [`map.assign`](#method-map-assign) accept array-like objects exposing getters and setters for array element access (e.g., [`Complex64Array`][@stdlib/array/complex64], [`Complex128Array`][@stdlib/array/complex128], etc). ```javascript var Complex64Array = require( '@stdlib/array-complex64' ); var Complex64 = require( '@stdlib/complex-float32-ctor' ); var realf = require( '@stdlib/complex-float32-real' ); var imagf = require( '@stdlib/complex-float32-imag' ); function scale( z ) { return new Complex64( realf(z)*10.0, imagf(z)*10.0 ); } var x = new Complex64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] ); var y = new Complex64Array( 4 ); map.assign( x, y, scale ); var v = y.get( 0 ); var re = realf( v ); // returns 10.0 var im = imagf( v ); // returns 20.0 ``` - When applying a function to [`ndarray`][@stdlib/ndarray/ctor]-like objects, performance will be best for [`ndarray`][@stdlib/ndarray/ctor]-like objects which are single-segment contiguous. For non-contiguous arrays, see [`@stdlib/ndarray-base/unary`][@stdlib/ndarray/base/unary]. - Both [`map`](#fcn-map) and [`map.assign`](#method-map-assign) do **not** skip `undefined` elements.

## Examples ```javascript var filledarrayBy = require( '@stdlib/array-filled-by' ); var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory; var naryFunction = require( '@stdlib/utils-nary-function' ); var abs2 = require( '@stdlib/math-base-special-abs2' ); var array = require( '@stdlib/ndarray-array' ); var map = require( '@stdlib/utils-map' ); function fill( i ) { var rand = discreteUniform( -10*(i+1), 10*(i+1) ); return filledarrayBy( 10, 'generic', rand ); } // Create a two-dimensional ndarray (i.e., a matrix): var x = array( filledarrayBy( 10, 'generic', fill ), { 'dtype': 'generic', 'flatten': true }); // Create an explicit unary function: var f = naryFunction( abs2, 1 ); // Compute the element-wise squared absolute value... var y = map( x, f ); console.log( 'x:' ); console.log( x.data ); console.log( 'y:' ); console.log( y.data ); ```

* * * ## 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].

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Name: stdlib
Login: stdlib-js
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Website: https://stdlib.io
Twitter: stdlibjs
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Standard library for JavaScript.

Citation (CITATION.cff)

cff-version: 1.2.0
title: stdlib
message: >-
  If you use this software, please cite it using the
  metadata from this file.

type: software

authors:
  - name: The Stdlib Authors
    url: https://github.com/stdlib-js/stdlib/graphs/contributors

repository-code: https://github.com/stdlib-js/stdlib
url: https://stdlib.io

abstract: |
  Standard library for JavaScript and Node.js.

keywords:
  - JavaScript
  - Node.js
  - TypeScript
  - standard library
  - scientific computing
  - numerical computing
  - statistical computing

license: Apache-2.0 AND BSL-1.0

date-released: 2016

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npmjs.org: @stdlib/utils-map

Apply a function to each element in an array and assign the result to an element in an output array.

Homepage: https://stdlib.io
License: Apache-2.0
Latest release: 0.2.1
published almost 2 years ago

Versions: 4
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Downloads: 18 Last month

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@stdlib/math-base-special-pow ^0.0.x development
@stdlib/ndarray-array ^0.0.x development
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@stdlib/random-base-discrete-uniform ^0.0.x development
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istanbul ^0.4.1 development
tap-spec 5.x.x development
tape git+https://github.com/kgryte/tape.git#fix/globby development
@stdlib/array-base-arraylike2object ^0.0.x
@stdlib/array-base-zeros ^0.0.x
@stdlib/assert-is-array-like-object ^0.0.x
@stdlib/assert-is-function ^0.0.x
@stdlib/assert-is-ndarray-like ^0.0.x
@stdlib/ndarray-base-assert-is-read-only ^0.0.x
@stdlib/ndarray-base-maybe-broadcast-array ^0.0.x
@stdlib/ndarray-base-ndarraylike2object ^0.0.x
@stdlib/ndarray-base-vind2bind ^0.0.x
@stdlib/ndarray-zeros ^0.0.x
@stdlib/string-format ^0.0.x
@stdlib/types ^0.0.x
@stdlib/utils-define-nonenumerable-read-only-property ^0.0.x

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