@stdlib/utils-for-each-right
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    0.0.7 • Public • Published

    forEachRight

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    Invoke a function for each element in a collection, iterating from the right to left.

    Installation

    npm install @stdlib/utils-for-each-right

    Usage

    var forEachRight = require( '@stdlib/utils-for-each-right' );

    forEachRight( collection, fcn[, thisArg ] )

    Invokes a function for each element in a collection, iterating from right to left.

    function log( value, index ) {
        console.log( '%s: %d', index, value );
    }
    
    var arr = [ 1, 2, 3, 4 ];
    
    forEachRight( arr, log );
    /* =>
        3: 4
        2: 3
        1: 2
        0: 1
    */

    The invoked function is provided three arguments:

    • value: collection element
    • index: collection index
    • collection: input collection

    Basic support for dynamic collections is provided. Note, however, that index incrementation is not guaranteed to be monotonically decreasing.

    var arr = [ 1, 2, 3, 4 ];
    var i = 0;
    
    function log1( value, index, collection ) {
        console.log( '%s: %d', index, value );
        i += 1;
        if ( index === 0 && collection.length < 10 ) {
            collection.unshift( i+1 );
        }
    }
    
    forEachRight( arr, log1 );
    /* =>
        3: 4
        2: 3
        1: 2
        0: 1
        0: 5
        0: 6
        0: 7
        0: 8
        0: 9
        0: 10
    */
    
    function log2( value, index, collection ) {
        console.log( '%s: %d', index, value );
        collection.pop();
    }
    
    arr = [ 1, 2, 3, 4 ];
    
    forEachRight( arr, log2 );
    /* =>
        3: 4
        1: 2
    */

    To set the function execution context, provide a thisArg.

    function sum( value ) {
        this.sum += value;
        this.count += 1;
    }
    
    var arr = [ 1, 2, 3, 4 ];
    
    var context = {
        'sum': 0,
        'count': 0
    };
    
    forEachRight( arr, sum, context );
    
    var mean = context.sum / context.count;
    // returns 2.5

    Notes

    • A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).

    • The function differs from Array.prototype.forEach in the following ways:

      • The function returns the input collection.

      • The function does not skip undefined elements.

        function log( value, index ) {
            console.log( '%s: %s', index, value );
        }
        
        var arr = [ 1, , , 4 ];
        
        forEachRight( arr, log );
        /* =>
            3: 4
            2: undefined
            1: undefined
            0: 1
        */
      • The function provides limited support for dynamic collections (i.e., collections whose length changes during execution).

    Examples

    var isEven = require( '@stdlib/assert-is-even' ).isPrimitive;
    var forEachRight = require( '@stdlib/utils-for-each-right' );
    
    var arr;
    var i;
    
    function log( value, index, collection ) {
        console.log( '%s: %d', index, value );
        i += 1;
        if ( isEven( i ) ) {
            collection.pop();
        } else {
            collection.unshift( i+1 );
        }
    }
    
    arr = new Array( 100 );
    for ( i = arr.length-1; i >= 0; i-- ) {
        arr[ i ] = i;
    }
    
    i = 0;
    forEachRight( arr, log );

    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.

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    License

    See LICENSE.

    Copyright

    Copyright © 2016-2021. The Stdlib Authors.

    Install

    npm i @stdlib/utils-for-each-right

    Homepage

    stdlib.io

    DownloadsWeekly Downloads

    3

    Version

    0.0.7

    License

    Apache-2.0

    Unpacked Size

    41.7 kB

    Total Files

    9

    Last publish

    Collaborators

    • stdlib-bot
    • kgryte
    • planeshifter
    • rreusser