someBy

    Test whether a collection contains at least n elements which pass a test implemented by a predicate function.

    Usage

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

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

    Tests whether a collection contains at least n elements which pass a test implemented by a predicate function.

    function isNegative( value ) {
        return ( value < 0 );
    }
    
    var arr = [ 1, -2, 3, 4, -1 ];
    
    var bool = someBy( arr, 2, isNegative );
    // returns true
    

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

    function isPositive( value ) {
        if ( value < 0 ) {
            throw new Error( 'should never reach this line' );
        }
        return ( value > 0 );
    }
    
    var arr = [ 1, 2, -3, 4 ];
    
    var bool = someBy( arr, 2, isPositive );
    // 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 = [ 1, 2, 3, 4, -5 ];
    
    var context = {
        'sum': 0,
        'count': 0
    };
    
    var bool = someBy( 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 = someBy( [], 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, , , 4, -1 ];
      
      var bool = someBy( arr, 1, log );
      /* =>
          0: 1
          1: undefined
          2: undefined
          3: 4
          4: -1
      */
      
    • The function provides limited support for dynamic collections (i.e., collections whose length changes during execution).

    Examples

    var randu = require( '@stdlib/random/base/randu' );
    var someBy = require( '@stdlib/utils/some-by' );
    
    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 = someBy( arr, 5, threshold );
    // returns <boolean>