someByRight

Test whether a collection contains at least n elements which pass a test implemented by a predicate function, iterating from right to left.

Usage

var someByRight = require( '@stdlib/utils/some-by-right' );

someByRight( collection, n, predicate[, thisArg ] )

Tests whether a collection contains at least n elements which pass a test implemented by a predicate function, iterating from right to left.

function isNegative( value ) {
    return ( value < 0 );
}

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

var bool = someByRight( arr, 2, isNegative );
// returns true

Once the function finds n successful elements, the function immediately returns true.

function isNegative( value ) {
    if ( value > 0 ) {
        throw new Error( 'should never reach this line' );
    }
    return ( value < 0 );
}

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

var bool = someByRight( arr, 2, isNegative );
// returns true

The invoked function is provided three arguments:

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

To set the function execution context, provide a thisArg.

function sum( value ) {
    this.sum += value;
    this.count += 1;
    return ( value < 0 );
}

var arr = [ -5, 1, 2, 3, 4 ];

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

var bool = someByRight( arr, 1, sum, context );
// returns true

var mean = context.sum / context.count;
// returns 1.0

Notes

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

  • If provided an empty collection, the function returns false.

    function alwaysTrue() {
        return true;
    }
    var bool = someByRight( [], 1, alwaysTrue );
    // returns false
    
  • The function does not skip undefined elements.

    function log( value, index ) {
        console.log( '%s: %s', index, value );
        return ( value < 0 );
    }
    
    var arr = [ -1, 1, , , 4 ];
    
    var bool = someByRight( arr, 1, log );
    /* =>
        4: 4
        3: undefined
        2: undefined
        1: 1
        0: -1
    */
    
  • The function provides limited support for dynamic collections (i.e., collections whose length changes during execution). Note, however, that index incrementation is not guaranteed to be monotonically decreasing.

Examples

var randu = require( '@stdlib/random/base/randu' );
var someByRight = require( '@stdlib/utils/some-by-right' );

function threshold( value ) {
    return ( value > 0.95 );
}

var bool;
var arr;
var i;

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

bool = someByRight( arr, 5, threshold );
// returns <boolean>