npm package: @stdlib/iter-filter
Description: Create an iterator which filters the values of another iterator according to a predicate function.
Author: The Stdlib Authors
Latest version: 0.2.3

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<details>
  <summary>
    About stdlib...
  </summary>
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</details>

# iterFilter

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

> Create an [iterator][mdn-iterator-protocol] which filters the values of another [iterator][mdn-iterator-protocol] according to a predicate function.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/iter-filter
```

</section>

<section class="usage">

## Usage

```javascript
var iterFilter = require( '@stdlib/iter-filter' );
```

#### iterFilter( iterator, predicate\[, thisArg] )

Returns an [iterator][mdn-iterator-protocol] which filters the values of another [`iterator`][mdn-iterator-protocol] according to a `predicate` function.

```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );

function predicate( v ) {
    return ( v > 2 );
}

var it = iterFilter( array2iterator( [ 1, 3, 2, 4 ] ), predicate );
// returns <Object>

var v = it.next().value;
// returns 3

v = it.next().value;
// returns 4

var bool = it.next().done;
// returns true
```

The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties:

-   **next**: function which returns an [iterator][mdn-iterator-protocol] protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the [iterator][mdn-iterator-protocol] is finished.
-   **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object.

The `predicate` function is provided two arguments:

-   **value**: iterated value.
-   **index**: iteration index (zero-based).

```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );

function predicate( v, i ) {
    return ( i >= 2 );
}

var it = iterFilter( array2iterator( [ 3, 4, 1, 2 ] ), predicate );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

var bool = it.next().done;
// returns true
```

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

<!-- eslint-disable no-invalid-this -->

```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );

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

var ctx = {
    'count': 0
};

var it = iterFilter( array2iterator( [ 1, 2, 3, 4 ] ), predicate, ctx );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

v = it.next().value;
// returns 3

var count = ctx.count;
// returns 3
```

</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 an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random-iter-randu' );
var iterFilter = require( '@stdlib/iter-filter' );

function predicate( v ) {
    return ( v > 0.5 );
}

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 20
});

// Create an iterator which filters the generated numbers:
var it = iterFilter( rand, predicate );

// Perform manual iteration...
var r;
while ( true ) {
    r = it.next();
    if ( r.done ) {
        break;
    }
    console.log( r.value );
}
```

</section>

<!-- /.examples -->

<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="references">

</section>

<!-- /.references -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/iter-filter-map`][@stdlib/iter/filter-map]</span><span class="delimiter">: </span><span class="description">create an iterator which both filters and maps the values of another iterator.</span>
-   <span class="package-name">[`@stdlib/iter-map`][@stdlib/iter/map]</span><span class="delimiter">: </span><span class="description">create an iterator which invokes a function for each iterated value.</span>
-   <span class="package-name">[`@stdlib/iter-reject`][@stdlib/iter/reject]</span><span class="delimiter">: </span><span class="description">create an iterator which rejects the values of another iterator according to a predicate function.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<section class="main-repo" >

* * *

## 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].

</section>

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[npm-url]: https://npmjs.org/package/@stdlib/iter-filter

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[test-url]: https://github.com/stdlib-js/iter-filter/actions/workflows/test.yml?query=branch:v0.2.3

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/iter-filter/tree/deno
[deno-readme]: https://github.com/stdlib-js/iter-filter/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/iter-filter/tree/umd
[umd-readme]: https://github.com/stdlib-js/iter-filter/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/iter-filter/tree/esm
[esm-readme]: https://github.com/stdlib-js/iter-filter/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/iter-filter/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/iter-filter/main/LICENSE

[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

<!-- <related-links> -->

[@stdlib/iter/filter-map]: https://www.npmjs.com/package/@stdlib/iter-filter-map

[@stdlib/iter/map]: https://www.npmjs.com/package/@stdlib/iter-map

[@stdlib/iter/reject]: https://www.npmjs.com/package/@stdlib/iter-reject

<!-- </related-links> -->

</section>

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