doUntilEachRight

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

    Usage

    var doUntilEachRight = require( '@stdlib/utils/do-until-each-right' );
    

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

    Invokes a function for each element in a collection, iterating from right to left, until either a predicate function returns true 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 ];
    
    doUntilEachRight( 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 = [];
    
    doUntilEachRight( 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 );
        }
    }
    
    doUntilEachRight( 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 ];
    
    doUntilEachRight( 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 < 3 );
    }
    
    function sum( value ) {
        this.sum += value;
        this.count += 1;
    }
    
    var arr = [ 1, NaN, 2, 3, 4 ];
    
    var context = {
        'sum': 0,
        'count': 0
    };
    
    doUntilEachRight( 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 ];
      
      doUntilEachRight( 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 doUntilEachRight = require( '@stdlib/utils/do-until-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;
    doUntilEachRight( arr, log, predicate );