inmapRight

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

    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 );