inmapRight

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

Installation

npm install @stdlib/utils-inmap-right

Usage

var inmapRight = require( '@stdlib/utils-inmap-right' );

inmapRight( collection, fcn[, thisArg ] )

Invokes a function for each element in a collection and updates the collection in-place, iterating from right to left.

function scale( value, index ) {
    return value * index;
}

var arr = [ 1, 2, 3, 4 ];

var out = inmapRight( arr, scale );
// returns [ 0, 2, 6, 12 ]

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

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 scale1( value, index, collection ) {
    i += 1;
    if ( index === 0 && collection.length < 10 ) {
        collection.unshift( i+1 );
    }
    return value * index;
}

var out = inmapRight( arr, scale1 );
// returns [ 0, 0, 0, 0, 0, 0, 0, 2, 6, 12 ]

function scale2( value, index, collection ) {
    collection.shift();
    return value * index;
}

arr = [ 1, 2, 3, 4 ];

out = inmapRight( arr, scale2 );
// returns [ 3, 12 ]

To set the function execution context, provide a thisArg.

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

var arr = [ 1, 2, 3, 4 ];

var context = {
    'sum': 0,
    'count': 0
};

var out = inmapRight( arr, sum, context );
// returns [ 1, 2, 3, 4 ]

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.map in the following ways:

  • The function returns the input collection.

  • The function modifies collection elements in-place.

  • The function does not skip undefined elements.

    function log( value, index ) {
        console.log( '%s: %s', index, value );
        return value;
    }
    
    var arr = [ 1, , , 4 ];
    
    var out = inmapRight( 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 inmapRight = require( '@stdlib/utils-inmap-right' );

var bool;
var arr;
var out;
var i;

function scale( value, index, collection ) {
    i += 1;
    if ( isEven( i ) ) {
        collection.pop();
    } else {
        collection.unshift( i+1 );
    }
    return value * index;
}

arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
    arr[ i ] = i;
}

i = 0;
out = inmapRight( arr, scale );

bool = ( out === arr );
console.log( bool );

console.log( out );

See Also

• @stdlib/utils-for-each-right: invoke a function for each element in a collection, iterating from right to left.
• @stdlib/utils-inmap: invoke a function for each element in a collection and update the collection in-place.
• @stdlib/utils-map-right: apply a function to each element in an array and assign the result to an element in an output array, iterating from right to left.

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

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.