@stdlib/utils-do-while-each-right
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0.2.1 • Public • Published
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doWhileEachRight

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While a test condition is true, invoke a function for each element in a collection, iterating from right to left.

Installation

npm install @stdlib/utils-do-while-each-right

Usage

var doWhileEachRight = require( '@stdlib/utils-do-while-each-right' );

doWhileEachRight( collection, fcn, predicate[, thisArg ] )

Invokes a function for each element in a collection, iterating from right to left, until either a predicate function returns false or the function has iterated over all collection elements. Note that the condition is evaluated after executing fcn; thus, fcn always executes at least once.

function predicate( value ) {
    return ( value === value );
}

function log( value, index ) {
    console.log( '%s: %d', index, value );
}

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

doWhileEachRight( arr, log, predicate );
/* =>
    4: 4
    3: 3
    2: 2
    1: NaN
*/

Both the predicate function and the function to apply are provided three arguments:

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

If provided an empty collection, both value and index are undefined.

function predicate( value ) {
    return ( value === value );
}

function log( value, index ) {
    console.log( '%s: %s', index, value );
}

var arr = [];

doWhileEachRight( arr, log, predicate );
/* =>
    undefined: undefined
*/

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 predicate( value ) {
    return ( value === value );
}

function log1( value, index, collection ) {
    console.log( '%s: %d', index, value );
    i += 1;
    if ( index === 0 && collection.length < 10 ) {
        collection.unshift( i+1 );
    }
}

doWhileEachRight( arr, log1, predicate );
/* =>
    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 ];

doWhileEachRight( arr, log2, predicate );
/* =>
    3: 4
    1: 2
*/

To set the function execution context for the applied function, provide a thisArg.

function predicate( value ) {
    return ( value > 2 );
}

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

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

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

doWhileEachRight( arr, sum, predicate, context );

var mean = context.sum / context.count;
// returns 3.0

Notes

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

  • The function returns the input collection.

  • The function does not skip undefined elements.

    function predicate( value ) {
        return ( value === value );
    }
    
    function log( value, index ) {
        console.log( '%s: %s', index, value );
    }
    
    var arr = [ 1, , , 4 ];
    
    doWhileEachRight( arr, log, predicate );
    /* =>
        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 randu = require( '@stdlib/random-base-randu' );
var floor = require( '@stdlib/math-base-special-floor' );
var doWhileEachRight = require( '@stdlib/utils-do-while-each-right' );

var arr;
var i;
var j;

function predicate( value ) {
    return ( value === value );
}

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 );
j = floor( randu()*arr.length );
for ( i = arr.length-1; i >= 0; i-- ) {
    if ( i === j ) {
        arr[ i ] = NaN;
    } else {
        arr[ i ] = i;
    }
}

i = 0;
doWhileEachRight( arr, log, predicate );

See Also


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 © 2016-2024. The Stdlib Authors.

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