@stdlib/iter/union/README.md

Standard iterator utilities.

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# iterUnion

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

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## 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.

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## 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.

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## 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 );
}
```

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* * *

## 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>

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

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[@stdlib/iter/intersection]: https://github.com/stdlib-js/iter/tree/main/intersection

[@stdlib/iter/unique]: https://github.com/stdlib-js/iter/tree/main/unique

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