npm package: @stdlib/array-base-flatten2d
Description: Flatten a two-dimensional nested array.
Author: The Stdlib Authors
Latest version: 0.2.3

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# flatten2d

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

> Flatten a two-dimensional nested array.

<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-flatten2d
```

</section>

<section class="usage">

## Usage

```javascript
var flatten2d = require( '@stdlib/array-base-flatten2d' );
```

#### flatten2d( x, shape, colexicographic )

Flattens a two-dimensional nested array.

```javascript
var x = [ [ 1, 2 ], [ 3, 4 ] ];

var out = flatten2d( x, [ 2, 2 ], false );
// returns [ 1, 2, 3, 4 ]
```

To flatten in colexicographic order, provide a third argument equal to `true`.

```javascript
var x = [ [ 1, 2 ], [ 3, 4 ] ];

var out = flatten2d( x, [ 2, 2 ], true );
// returns [ 1, 3, 2, 4 ]
```

#### flatten2d.assign( x, shape, colexicographic, out, stride, offset )

Flattens a two-dimensional nested array and assigns elements to a provided output array.

```javascript
var Float64Array = require( '@stdlib/array-float64' );

var x = [ [ 1, 2 ], [ 3, 4 ] ];
var out = new Float64Array( 4 );

var y = flatten2d.assign( x, [ 2, 2 ], false, out, 1, 0 );
// returns <Float64Array>[ 1, 2, 3, 4 ]

var bool = ( y === out );
// returns true

y = flatten2d.assign( x, [ 2, 2 ], true, out, 1, 0 );
// returns <Float64Array>[ 1, 3, 2, 4 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   Both functions assume that all nested arrays have the same length (i.e., the input array is **not** a ragged array).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var flatten2d = require( '@stdlib/array-base-flatten2d' );

var x = [
    [ 1, 2, 3, 4 ],
    [ 5, 6, 7, 8 ],
    [ 9, 10, 11, 12 ],
    [ 13, 14, 15, 16 ]
];

var out = flatten2d( x, [ 0, 0 ], false );
// returns []

out = flatten2d( x, [ 0, 0 ], true );
// returns []

out = flatten2d( x, [ 1, 1 ], false );
// returns [ 1 ]

out = flatten2d( x, [ 1, 1 ], true );
// returns [ 1 ]

out = flatten2d( x, [ 2, 2 ], false );
// returns [ 1, 2, 5, 6 ]

out = flatten2d( x, [ 2, 2 ], true );
// returns [ 1, 5, 2, 6 ]

out = flatten2d( x, [ 3, 3 ], false );
// returns [ 1, 2, 3, 5, 6, 7, 9, 10, 11 ]

out = flatten2d( x, [ 3, 3 ], true );
// returns [ 1, 5, 9, 2, 6, 10, 3, 7, 11 ]

out = flatten2d( x, [ 4, 4 ], false );
// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ]

out = flatten2d( x, [ 4, 4 ], true );
// returns [ 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15, 4, 8, 12, 16 ]
```

</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/array-base/flatten2d-by`][@stdlib/array/base/flatten2d-by]</span><span class="delimiter">: </span><span class="description">flatten a two-dimensional nested array according to a callback function.</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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</section>

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