@stdlib/utils-every-by

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everyBy

Test whether all elements in a collection pass a test implemented by a predicate function.

Installation

npm install @stdlib/utils-every-by

Usage

var everyBy = require( '@stdlib/utils-every-by' );

everyBy( collection, predicate[, thisArg ] )

Tests whether all elements in a collection pass a test implemented by a predicate function.

function isPositive( value ) {
    return ( value > 0 );
}

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

var bool = everyBy( arr, isPositive );
// returns true

If a predicate function returns a non-truthy value, the function immediately returns false.

function isPositive( value ) {
    return ( value > 0 );
}

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

var bool = everyBy( arr, isPositive );
// returns false

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

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

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

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

var mean = context.sum / context.count;
// returns 2.5

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 true.

  function untrue() {
      return false;
  }
  var bool = everyBy( [], untrue );
  // returns true

• The function differs from Array.prototype.every in the following ways:

  • The function does not skip undefined elements.

    function log( value, index ) {
        console.log( '%s: %s', index, value );
        return true;
    }
    
    var arr = [ 1, , , 4 ];
    
    var bool = everyBy( arr, log );
    /* =>
        0: 1
        1: undefined
        2: undefined
        3: 4
    */

  • 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 everyBy = require( '@stdlib/utils-every-by' );

function isPositive( value ) {
    return ( value > 0 );
}

var bool;
var arr;
var i;

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

bool = everyBy( arr, isPositive );
// 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-right: test whether all elements in a collection pass a test implemented by a predicate function, iterating from right to left.
• @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-some-by: test whether a collection contains at least n elements which pass a test implemented by a predicate function.

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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.