npm package: @stdlib/iter-union
Description: Create an iterator which returns the union of two or more iterators.
Author: The Stdlib Authors
Latest version: 0.2.3

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  <summary>
    About stdlib...
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# iterUnion

[![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 returns the union of two or more [iterators][mdn-iterator-protocol].

<!-- 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-union
```

</section>

<section class="usage">

## Usage

```javascript
var iterUnion = require( '@stdlib/iter-union' );
```

#### iterUnion( iter0, ...iterator )

Returns an [iterator][mdn-iterator-protocol] which returns the union of two or more [iterators][mdn-iterator-protocol].

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

var it1 = array2iterator( [ 2, 1, 1, 2, 4 ] );
var it2 = array2iterator( [ 3, 4, 3 ] );

var it = iterUnion( it1, it2 );
// returns <Object>

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

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

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

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

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.

</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

-   Value "uniqueness" is determined according to **strict equality**.
-   A returned [iterator][mdn-iterator-protocol] internally buffers unique values and, thus, has `O(N)` memory requirements, where `N` is the total number of [iterator][mdn-iterator-protocol] source values.
-   If an environment supports `Symbol.iterator` **and** all provided [iterators][mdn-iterator-protocol] are iterable, the returned [iterator][mdn-iterator-protocol] is iterable.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-iter-discrete-uniform' );
var iterUnion = require( '@stdlib/iter-union' );

// Create seeded iterators which can generate 1000 pseudorandom numbers:
var rand1 = discreteUniform( 1, 10, {
    'seed': 1234,
    'iter': 1000
});
var rand2 = discreteUniform( 6, 15, {
    'seed': 1234,
    'iter': 1000
});

// Create an iterator which returns the union of the seeded iterators:
var it = iterUnion( rand1, rand2 );

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

</section>

<!-- /.examples -->

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<section class="references">

</section>

<!-- /.references -->

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/iter-intersection`][@stdlib/iter/intersection]</span><span class="delimiter">: </span><span class="description">create an iterator which returns the intersection of two or more iterators.</span>
-   <span class="package-name">[`@stdlib/iter-unique`][@stdlib/iter/unique]</span><span class="delimiter">: </span><span class="description">create an iterator which returns unique values.</span>

</section>

<!-- /.related -->

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<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>

<!-- /.stdlib -->

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[npm-image]: http://img.shields.io/npm/v/@stdlib/iter-union.svg
[npm-url]: https://npmjs.org/package/@stdlib/iter-union

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

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[stdlib]: https://github.com/stdlib-js/stdlib

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

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

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

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

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

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

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

</section>

<!-- /.links -->