Flatten Array

Flatten an array.

Usage

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

flattenArray( arr[, options] )

Flattens an array.

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 array elements. Default: false.
• equalDims: boolean indicating whether all array elements have equal dimensions. Default: false.

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

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 array elements, set the copy option to true.

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

By default, the function handles the generic case in which a provided array may be heterogeneous (contain mixed data types) or have unknown dimensions. If all array elements are known to have the same dimensions, setting the equalDims option to true allows the implementation to make performance optimizations.

// All elements are 1x3...
var arr = [
    [ [  1,  2,  3 ] ],
    [ [  4,  5,  6 ] ],
    [ [  7,  8,  9 ] ],
    [ [ 10, 11, 12 ] ]
];

var out = flattenArray( arr, {
    'equalDims': true
});
// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ]

flattenArray.factory( dims[, options] )

Returns a function optimized for flattening arrays having specified dimensions.

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 array elements. Default: false.

To deep copy array elements, set the copy option to true.

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

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

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

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

Notes

• A flatten function returned by the factory method does not validate that input arrays actually have the specified dimensions.

Examples

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

var xStride;
var yStride;
var zStride;
var tmp1;
var tmp2;
var arr;
var val;
var out;
var N;
var M;
var L;
var i;
var j;
var k;

N = 1000;
M = 100;
L = 10;

// Create an NxMxL (3D) array...
arr = new Array( N );
for ( i = 0; i < N; i++ ) {
    tmp1 = new Array( M );
    for ( j = 0; j < M; j++ ) {
        tmp2 = new Array( L );
        for ( k = 0; k < L; k++ ) {
            tmp2[ k ] = (M*L*i) + (j*L) + k + 1;
        }
        tmp1[ j ] = tmp2;
    }
    arr[ i ] = tmp1;
}
// Create a flattened (strided) array:
out = flattenArray( arr );

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

bool = ( arr[4][20][2] === val );
// returns true