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map

Apply a callback function to elements in an input array and assign results to elements in a new output array.

Installation

npm install @stdlib/array-base-map

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md 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

var map = require( '@stdlib/array-base-map' );

map( x, fcn[, thisArg] )

Applies a callback function to elements in an input array and assigns results to elements in a new output array.

var naryFunction = require( '@stdlib/utils-nary-function' );
var abs = require( '@stdlib/math-base-special-abs' );

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

var y = map( x, naryFunction( abs, 1 ) );
// returns [ 1.0, 2.0, 3.0, 4.0 ]

The function accepts the following arguments:

• x: input array.
• fcn: callback function.
• thisArg: callback execution context (optional).

To set the callback function's execution context, provide a thisArg.

function count( x ) {
    this.count += 1;
    return x;
}

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

var ctx = {
    'count': 0
};

var y = map( x, count, ctx );
// returns [ 1.0, 2.0, 3.0, 4.0 ]

var v = ctx.count;
// returns 4

The callback function is provided the following arguments:

• value: current array element.
• index: current element index.
• arr: input array.

map.assign( x, y, stride, offset, fcn[, thisArg] )

Applies a callback function to elements in an input array and assigns results to elements in an output array.

var naryFunction = require( '@stdlib/utils-nary-function' );
var zeros = require( '@stdlib/array-base-zeros' );
var abs = require( '@stdlib/math-base-special-abs' );

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

var y = zeros( x.length );

var out = map.assign( x, y, 1, 0, naryFunction( abs, 1 ) );
// returns [ 1.0, 2.0, 3.0, 4.0 ]

var bool = ( out === y );
// returns true

The function accepts the following arguments:

• x: input array.
• y: output array.
• stride: stride length for output array.
• offset: starting index for output array.
• fcn: callback function.
• thisArg: callback execution context (optional).

Notes

• If provided an array-like object having a map method, the function defers execution to that method and assumes that the method API has the following signature:

  x.map( fcn, thisArg )
  

• The function supports array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array-base/accessor).

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var naryFunction = require( '@stdlib/utils-nary-function' );
var abs = require( '@stdlib/math-base-special-abs' );
var map = require( '@stdlib/array-base-map' );

var x = discreteUniform( 10, -10, 10, {
    'dtype': 'float64'
});

var y = map( x, naryFunction( abs, 1 ) );
console.log( y );

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Notice

This package is part of 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, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.