npm package: @stdlib/array-base-count-if
Description: Count the number of elements in an array which pass a test implemented by a predicate function.
Author: The Stdlib Authors
Latest version: 0.1.2

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# countIf

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

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

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

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

</section>

<section class="usage">

## Usage

```javascript
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.

```javascript
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`.

```javascript
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
```

</section>

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<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
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 );
```

</section>

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* * *

## Notice

This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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