# @stdlib/array-base-flatten2d-by

0.2.0 • Public • Published

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# flatten2dBy

Flatten a two-dimensional nested array according to a callback function.

## Installation

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

## Usage

`var flatten2dBy = require( '@stdlib/array-base-flatten2d-by' );`

#### flatten2dBy( x, shape, colexicographic, clbk[, thisArg] )

Flattens a two-dimensional nested array according to a callback function.

```function scale( v ) {
return v * 2;
}

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

var out = flatten2dBy( x, [ 2, 2 ], false, scale );
// returns [ 2, 4, 6, 8 ]```

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

```function scale( v ) {
return v * 2;
}

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

var out = flatten2dBy( x, [ 2, 2 ], true, scale );
// returns [ 2, 6, 4, 8 ]```

To set the callback execution context, provide a `thisArg` argument.

```function scale( v ) {
this.count += 1;
return v * 2;
}

var x = [ [ 1, 2 ], [ 3, 4 ] ];
var ctx = {
'count': 0
};

var out = flatten2dBy( x, [ 2, 2 ], false, scale, ctx );
// returns [ 2, 4, 6, 8 ]

var count = ctx.count;
// returns 4```

#### flatten2dBy.assign( x, shape, colexicographic, out, stride, offset, clbk[, thisArg] )

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

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

function scale( v ) {
return v * 2;
}

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

var y = flatten2dBy.assign( x, [ 2, 2 ], false, out, 1, 0, scale );
// returns <Float64Array>[ 2, 4, 6, 8 ]

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

y = flatten2dBy.assign( x, [ 2, 2 ], true, out, 1, 0, scale );
// returns <Float64Array>[ 2, 6, 4, 8 ]```

## Notes

• A callback function is provided the following arguments:

• value: nested array element.
• indices: element indices (in lexicographic order).
• arr: the input array.
• Both functions assume that all nested arrays have the same length (i.e., the input array is not a ragged array).

## Examples

```var naryFunction = require( '@stdlib/utils-nary-function' );
var abs = require( '@stdlib/math-base-special-abs' );
var flatten2dBy = require( '@stdlib/array-base-flatten2d-by' );

var fcn = naryFunction( abs, 1 );

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

var out = flatten2dBy( x, [ 0, 0 ], false, fcn );
// returns []

out = flatten2dBy( x, [ 0, 0 ], true, fcn );
// returns []

out = flatten2dBy( x, [ 1, 1 ], false, fcn );
// returns [ 1 ]

out = flatten2dBy( x, [ 1, 1 ], true, fcn );
// returns [ 1 ]

out = flatten2dBy( x, [ 2, 2 ], false, fcn );
// returns [ 1, 2, 5, 6 ]

out = flatten2dBy( x, [ 2, 2 ], true, fcn );
// returns [ 1, 5, 2, 6 ]

out = flatten2dBy( x, [ 3, 3 ], false, fcn );
// returns [ 1, 2, 3, 5, 6, 7, 9, 10, 11 ]

out = flatten2dBy( x, [ 3, 3 ], true, fcn );
// returns [ 1, 5, 9, 2, 6, 10, 3, 7, 11 ]

out = flatten2dBy( x, [ 4, 4 ], false, fcn );
// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ]

out = flatten2dBy( x, [ 4, 4 ], true, fcn );
// returns [ 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15, 4, 8, 12, 16 ]```

## Notice

This package is part of 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, see the main project repository.

## Package Sidebar

### Install

`npm i @stdlib/array-base-flatten2d-by`

### Repository

github.com/stdlib-js/array-base-flatten2d-by

stdlib.io

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