npm package: @stdlib/array-base-filter
Description: Return a shallow copy of an array containing only those elements which pass a test implemented by a predicate function.
Author: The Stdlib Authors
Latest version: 0.2.3

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# filter

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

> Return a shallow copy of an array containing only those elements 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-filter
```

</section>

<section class="usage">

## Usage

```javascript
var filter = require( '@stdlib/array-base-filter' );
```

#### filter( x, predicate\[, thisArg] )

Returns a shallow copy of an array containing only those elements which pass a test implemented by a `predicate` function.

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

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

var out = filter( x, isPositive );
// returns [ 1, 4 ]
```

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

var context = {
    'count': 0
};

var out = filter( x, predicate, context );
// returns [ 1, 2, 4 ]

var cnt = context.count;
// returns 4
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   If provided an array-like object having a `filter` method, the function defers execution to that method and assumes that the method API has the following signature:

    ```text
    x.filter( predicate, thisArg )
    ```

-   If provided an array-like object without a `filter` method, the function performs a linear scan and **always** returns a generic array.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<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 filter = require( '@stdlib/array-base-filter' );

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

var out = filter( x, naryFunction( isPositiveInteger, 1 ) );
// returns <Int32Array>
```

</section>

<!-- /.examples -->

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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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