All files / reverse-dimensions/lib main.js

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/**
* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
 
'use strict';
 
// MODULES //
 
var args2multislice = require( '@stdlib/slice/base/args2multislice' );
var Slice = require( '@stdlib/slice/ctor' );
var slice = require( '@stdlib/ndarray/base/slice' );
var nulls = require( '@stdlib/array/base/nulls' );
var ndims = require( '@stdlib/ndarray/base/ndims' );
var toUniqueNormalizedIndices = require( '@stdlib/ndarray/base/to-unique-normalized-indices' );
var join = require( '@stdlib/array/base/join' );
var format = require( '@stdlib/string/format' );
 
 
// MAIN //
 
/**
* Returns a view of an input ndarray in which the order of elements along specified dimensions is reversed.
*
* @param {ndarray} x - input array
* @param {IntegerArray} dims - indices of dimensions to reverse
* @param {boolean} writable - boolean indicating whether a returned array should be writable
* @throws {TypeError} first argument must be an ndarray having one or more dimensions
* @throws {RangeError} dimension index exceeds the number of dimensions
* @throws {Error} must provide unique dimension indices
* @returns {ndarray} ndarray view
*
* @example
* var array = require( '@stdlib/ndarray/array' );
*
* var x = array( [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] );
* // returns <ndarray>[ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]
*
* var y = reverseDimensions( x, [ 0, 1 ], false );
* // returns <ndarray>[ [ 6.0, 5.0 ], [ 4.0, 3.0 ], [ 2.0, 1.0 ] ]
*/
function reverseDimensions( x, dims, writable ) {
	var args;
	var N;
	var d;
	var i;

	// Retrieve the number of array dimensions:
	N = ndims( x );

	// Check whether we were provided a zero-dimensional array...
	if ( N === 0 ) {
		throw new TypeError( format( 'invalid argument. First argument must be an ndarray having one or more dimensions. Number of dimensions: %d.', N ) );
	}
	// Normalize the dimension indices...
	d = toUniqueNormalizedIndices( dims, N-1 );
	if ( d === null ) {
		throw new RangeError( format( 'invalid argument. Specified dimension index is out-of-bounds. Must be on the interval: [-%u, %u]. Value: `[%s]`.', N, N-1, join( dims, ', ' ) ) );
	}
	if ( d.length !== dims.length ) {
		throw new Error( format( 'invalid argument. Must provide unique dimension indices. Value: `[%s]`.', join( dims, ', ' ) ) );
	}
	// Define a list of MultiSlice constructor arguments:
	args = nulls( N );
	for ( i = 0; i < d.length; i++ ) {
		args[ d[ i ] ] = new Slice( null, null, -1 );
	}
	// Return a new array view:
	return slice( x, args2multislice( args ), true, writable );
}
 
 
// EXPORTS //
 
module.exports = reverseDimensions;