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maybeBroadcastArrayExceptDimensions

Broadcast an ndarray to a specified shape while keeping a list of specified dimensions unchanged if and only if the specified shape differs from the provided ndarray's shape.

Usage

var maybeBroadcastArrayExceptDimensions = require( '@stdlib/ndarray/base/maybe-broadcast-array-except-dimensions' );

maybeBroadcastArrayExceptDimensions( arr, shape, dims )

Broadcasts an ndarray to a specified shape while keeping a list of specified dimensions unchanged if and only if the specified shape differs from the provided ndarray's shape.

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

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

// Perform broadcasting:
var y = maybeBroadcastArrayExceptDimensions( x, [ 3, 2, 2 ], [ -1 ] );
// returns <ndarray>[ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 1, 2 ], [ 3, 4 ] ], [ [ 1, 2 ], [ 3, 4 ] ] ]

The function accepts the following arguments:

  • arr: input ndarray.
  • shape: target shape.
  • dims: list of dimensions to exclude from broadcasting. Should be a list of negative integers.

Notes

  • The function throws an error if a provided ndarray is incompatible with a provided shape.
  • If a provided ndarray has the same shape as the specified shape (excluding the list of specified dimensions), the function returns the provided ndarray.
  • If a provided ndarray has a different (broadcast compatible) shape than the specified shape, the function returns a new (base) ndarray view of the provided ndarray's data. The view is typically not contiguous. As more than one element of a returned view may refer to the same memory location, writing to the view may affect multiple elements. If you need to write to the returned ndarray, copy the ndarray before performing operations which may mutate elements.
  • If a provided ndarray does not have the same shape as the specified shape (excluding the list of specified dimensions), the returned ndarray is a "base" ndarray, and, thus, the returned ndarray does not perform bounds checking or afford any of the guarantees of the non-base ndarray constructor. The primary intent of this function is to broadcast an ndarray-like object within internal implementations and to do so with minimal overhead.

Examples

var array = require( '@stdlib/ndarray/array' );
var numel = require( '@stdlib/ndarray/base/numel' );
var ind2sub = require( '@stdlib/ndarray/ind2sub' );
var getShape = require( '@stdlib/ndarray/shape' );
var maybeBroadcastArrayExceptDimensions = require( '@stdlib/ndarray/base/maybe-broadcast-array-except-dimensions' );

// Create a 1x3 array:
var x = array( [ [ 1, 2, 3 ] ] );
// returns <ndarray>[ [ 1, 2, 3 ] ]

// Broadcast the array to 2x1x3:
var y = maybeBroadcastArrayExceptDimensions( x, [ 2, 2, 3 ], [ -2 ] );
// returns <ndarray>[ [ [ 1, 2, 3 ] ], [ [ 1, 2, 3 ] ] ]

// Retrieve the shape:
var sh = getShape( y );
// returns [ 2, 1, 3 ]

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

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