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countIf

Count the number of elements in an array which pass a test implemented by a predicate function.

Installation

npm install @stdlib/array-base-count-if

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 countIf = require( '@stdlib/array-base-count-if' );

countIf( x, predicate[, thisArg] )

Counts the number of elements in an array which pass a test implemented by a predicate function.

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

var x = [ 0, 1, 0, 1, 2 ];

var out = countIf( x, predicate );
// returns 3

The predicate function is provided three arguments:

• value: current array element.
• index: current array element index.
• arr: input array.

To set the predicate function execution context, provide a thisArg.

function predicate( value ) {
    this.count += 1;
    return ( value > 0 );
}

var x = [ 0, 1, 0, 1, 2 ];

var context = {
    'count': 0
};

var out = countIf( x, predicate, context );
// returns 3

var cnt = context.count;
// returns 5

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var isPositiveInteger = require( '@stdlib/assert-is-positive-integer' ).isPrimitive;
var naryFunction = require( '@stdlib/utils-nary-function' );
var countIf = require( '@stdlib/array-base-count-if' );

var x = discreteUniform( 10, -5, 5, {
    'dtype': 'int32'
});
// returns <Int32Array>

var out = countIf( x, naryFunction( isPositiveInteger, 1 ) );
// returns <number>

console.log( x );
console.log( out );

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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.