@stdlib/utils-some-by NPM

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

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>

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.