npm package: @stdlib/utils-flatten-array
Description: Flatten an array.
Author: The Stdlib Authors
Latest version: 0.2.3

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</details>

# flattenArray

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

> Flatten an array.

<section class="installation">

## Installation

```bash
npm install @stdlib/utils-flatten-array
```

</section>

<section class="usage">

## Usage

```javascript
var flattenArray = require( '@stdlib/utils-flatten-array' );
```

#### flattenArray( arr\[, options] )

Flattens an array.

```javascript
var arr = [ 1, [2, [3, [4, [ 5 ], 6], 7], 8], 9 ];

var out = flattenArray( arr );
// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
```

The function accepts the following `options`:

-   **depth**: maximum depth to flatten.
-   **copy**: `boolean` indicating whether to deep [copy][@stdlib/utils/copy] array elements. Default: `false`.

To flatten to a specified depth, set the `depth` option.

```javascript
var arr = [ 1, [2, [3, [4, [ 5 ], 6], 7], 8], 9 ];

var out = flattenArray( arr, {
    'depth': 2
});
// returns [ 1, 2, 3, [4, [5], 6], 7, 8, 9 ]

var bool = ( arr[1][1][1] === out[3] );
// returns true
```

To deep [copy][@stdlib/utils/copy] array elements, set the `copy` option to `true`.

```javascript
var arr = [ 1, [2, [3, [4, [ 5 ], 6], 7], 8], 9 ];

var out = flattenArray( arr, {
    'depth': 2,
    'copy': true
});
// returns [ 1, 2, 3, [4, [5], 6], 7, 8, 9 ]

var bool = ( arr[1][1][1] === out[3] );
// returns false
```

#### flattenArray.factory( dims\[, options] )

Returns a `function` optimized for flattening arrays having specified dimensions.

```javascript
var flatten = flattenArray.factory( [ 3, 3 ] );

var arr = [
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7, 8, 9 ]
];

var out = flatten( arr );
// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

arr = [
    [ 11, 12, 13 ],
    [ 14, 15, 16 ],
    [ 17, 18, 19 ]
];

out = flatten( arr );
// returns [ 11, 12, 13, 14, 15, 16, 17, 18, 19 ]
```

The function accepts the following `options`:

-   **copy**: `boolean` indicating whether to deep [copy][@stdlib/utils/copy] array elements. Default: `false`.

To deep [copy][@stdlib/utils/copy] array elements, set the `copy` option to `true`.

<!-- eslint-disable object-curly-newline -->

```javascript
var flatten = flattenArray.factory( [ 3, 3 ], {
    'copy': true
});

var arr = [
    [ 1, 2, 3 ],
    [ 4, { 'x': 5 }, 6 ],
    [ 7, 8, 9 ]
];

var out = flatten( arr );
// returns [ 1, 2, 3, 4, {'x':5}, 6, 7, 8, 9 ]

var bool = ( arr[1][1] === out[4] );
// returns false
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   A flatten `function` returned by the factory method does **not** validate that input `arrays` actually have the specified dimensions.
-   The `factory` method uses code evaluation, which may be problematic in browser contexts enforcing a strict [content security policy][mdn-csp] (CSP).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint-disable array-bracket-spacing -->

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

```javascript
var flattenArray = require( '@stdlib/utils-flatten-array' );

function tensor( N, M, L ) {
    var tmp1;
    var tmp2;
    var out;
    var i;
    var j;
    var k;

    out = [];
    for ( i = 0; i < N; i++ ) {
        tmp1 = [];
        for ( j = 0; j < M; j++ ) {
            tmp2 = [];
            for ( k = 0; k < L; k++ ) {
                tmp2.push( (M*L*i) + (j*L) + k + 1 );
            }
            tmp1.push( tmp2 );
        }
        out.push( tmp1 );
    }
    return out;
}

// Define array dimensions:
var N = 1000;
var M = 100;
var L = 10;

// Create a 3-dimensional nested array:
var data = tensor( N, M, L );

// Create a flattened (strided) array from a 3-dimensional nested array:
var arr = flattenArray( data );

// To access the data[4][20][2] element...
var xStride = M * L;
var yStride = L;
var zStride = 1;
var v = arr[ (4*xStride) + (20*yStride) + (2*zStride) ];
// returns 4203

var bool = ( data[4][20][2] === v );
// returns true
```

</section>

<!-- /.examples -->

<!-- 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/utils-flatten-object`][@stdlib/utils/flatten-object]</span><span class="delimiter">: </span><span class="description">flatten an object.</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>

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[@stdlib/utils/copy]: https://www.npmjs.com/package/@stdlib/utils-copy

[mdn-csp]: https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP

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

[@stdlib/utils/flatten-object]: https://www.npmjs.com/package/@stdlib/utils-flatten-object

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</section>

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