spreadDimensions

Expand the shape of an array to a specified dimensionality by spreading its dimensions to specified dimension indices and inserting dimensions of size one for the remaining dimensions.

Usage

var spreadDimensions = require( '@stdlib/ndarray/base/spread-dimensions' );

spreadDimensions( ndims, x, dims )

Expands the shape of an array to a specified dimensionality by spreading its dimensions to specified dimension indices and inserting dimensions of size one for the remaining dimensions.

var ndarray2array = require( '@stdlib/ndarray/to-array' );
var array = require( '@stdlib/ndarray/array' );

// Create a 2x2 ndarray:
var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
// returns <ndarray>

// Prepend a singleton dimension:
var y = spreadDimensions( 3, x, [ 1, 2 ] );
// returns <ndarray>

var sh = y.shape;
// returns [ 1, 2, 2 ]

var a = ndarray2array( y );
// returns [ [ [ 1, 2 ], [ 3, 4 ] ] ]

// Append a singleton dimension:
y = spreadDimensions( 3, x, [ 0, 1 ] );
// returns <ndarray>

sh = y.shape;
// returns [ 2, 2, 1 ]

a = ndarray2array( y );
// returns [ [ [ 1 ], [ 2 ] ], [ [ 3 ], [ 4 ] ] ]

// Insert a singleton dimension:
y = spreadDimensions( 3, x, [ 0, 2 ] );
// returns <ndarray>

sh = y.shape;
// returns [ 2, 1, 2 ]

a = ndarray2array( y );
// returns [ [ [ 1, 2 ] ], [ [ 3, 4 ] ] ]

Notes

Each provided dimension index must reside on the interval [-ndims, ndims-1]. If provided a negative dimension index, the position at which to place a respective dimension is computed as ndims + index.
Provided dimension indices must resolve to normalized dimension indices arranged in ascending order.

Examples

var array = require( '@stdlib/ndarray/array' );
var numel = require( '@stdlib/ndarray/base/numel' );
var ind2sub = require( '@stdlib/ndarray/ind2sub' );
var spreadDimensions = require( '@stdlib/ndarray/base/spread-dimensions' );

// Create a 2-dimensional array:
var x = array( [ [ 1, 2 ], [ 3, 4 ] ], {
    'order': 'column-major'
});
// returns <ndarray>

// Spread dimensions:
var y = spreadDimensions( 5, x, [ 1, 3 ] );
// returns <ndarray>

// Retrieve the shape:
var sh = y.shape;
// returns [ 1, 2, 1, 2, 1 ]

// Retrieve the number of elements:
var N = numel( sh );

// Loop through the array elements...
var i;
for ( i = 0; i < N; i++ ) {
    console.log( 'Y[%s] = %d', ind2sub( sh, i ).join( ', ' ), y.iget( i ) );
}