README.md

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someBy

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

Installation

npm install @stdlib/utils-some-by

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

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>

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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.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.