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>

See Also

• @stdlib/utils/any-by: test whether at least one element in a collection passes a test implemented by a predicate function.
• @stdlib/utils/every-by: test whether all elements in a collection pass a test implemented by a predicate function.
• @stdlib/utils/for-each: invoke a function for each element in a collection.
• @stdlib/utils/none-by: test whether all elements in a collection fail a test implemented by a predicate function.
• @stdlib/utils/async/some-by: test whether a collection contains n elements which pass a test implemented by a predicate function.
• @stdlib/utils/some-by-right: test whether a collection contains at least n elements which pass a test implemented by a predicate function, iterating from right to left.