whileEachRight

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

Usage

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

whileEachRight( collection, predicate, fcn[, 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.

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

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

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

whileEachRight( arr, predicate, log );
/* =>
    4: 4
    3: 3
    2: 2
*/

Both the predicate function and the function to apply are 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 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 );
    }
}

whileEachRight( arr, predicate, 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 ];

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

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

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

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

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

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

whileEachRight( arr, predicate, sum, 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 ];

whileEachRight( arr, predicate, 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 randu = require( '@stdlib/random/base/randu' );
var floor = require( '@stdlib/math/base/special/floor' );
var whileEachRight = require( '@stdlib/utils/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;
whileEachRight( arr, predicate, log );