@stdlib/utils/flatten-array/README.md

Standard utilities.

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# flattenArray

> Flatten an array.

<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 -->

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

<section class="links">

[@stdlib/utils/copy]: https://github.com/stdlib-js/utils/tree/main/copy

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

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

[@stdlib/utils/flatten-object]: https://github.com/stdlib-js/utils/tree/main/flatten-object

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

</section>

<!-- /.links -->