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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 isRowMajorString = require( '@stdlib/ndarray/base/assert/is-row-major-string' );
var strides2order = require( '@stdlib/ndarray/base/strides2order' );
var normalizeIndex = require( '@stdlib/ndarray/base/normalize-index' );
var getDType = require( '@stdlib/ndarray/base/dtype' );
var getShape = require( '@stdlib/ndarray/base/shape' );
var getStrides = require( '@stdlib/ndarray/base/strides' );
var getOffset = require( '@stdlib/ndarray/base/offset' );
var getOrder = require( '@stdlib/ndarray/base/order' );
var getData = require( '@stdlib/ndarray/base/data-buffer' );
var unflattenShape = require( '@stdlib/ndarray/base/unflatten-shape' );
// MAIN //
/**
* Returns a view of an input ndarray in which a specified dimension is expanded over multiple dimensions.
*
* @param {ndarray} x - input array
* @param {integer} dim - dimension index
* @param {NonNegativeIntegerArray} sizes - new shape of the unflattened dimension
* @param {boolean} writable - boolean indicating whether the returned ndarray should be writable
* @throws {RangeError} must provide a valid dimension index
* @throws {RangeError} product of the sizes must be equal to the size of the dimension to be unflattened
* @returns {ndarray} output array
*
* @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 out = unflatten( x, 0, [ 2, 3 ], false );
* // returns <ndarray>[ [ 1.0, 2.0, 3.0 ], [ 4.0, 5.0, 6.0 ] ]
*/
function unflatten( x, dim, sizes, writable ) {
var strides;
var shape;
var isrm;
var ord;
var sh;
var st;
var S2;
var o;
var d;
var i;
sh = getShape( x, false );
st = getStrides( x, false );
ord = getOrder( x );
o = strides2order( st );
if ( o === 0 || o === 3 ) {
// Fallback to stated layout when unable to infer the underlying physical layout:
isrm = isRowMajorString( ord );
} else {
isrm = ( o === 1 );
}
// Normalize the dimension to be unflattened:
d = normalizeIndex( dim, sh.length-1 );
// Compute the output shape:
shape = unflattenShape( sh, d, sizes );
// Resolve the output strides:
strides = [];
S2 = sizes.length;
for ( i = 0; i < d; i++ ) {
strides.push( st[ i ] );
}
for ( i = 0; i < S2; i++ ) {
strides.push( 0 );
}
for ( i = d+1; i < sh.length; i++ ) {
strides.push( st[ i ] );
}
// Compute strides for the unflattened dimensions...
if ( isrm ) {
strides[ d+S2-1 ] = st[ d ];
for ( i = S2-1; i > 0; i-- ) {
strides[ d+i-1 ] = strides[ d+i ] * sizes[ i ];
}
} else {
strides[ d ] = st[ d ];
for ( i = 0; i < S2-1; i++ ) {
strides[ d+i+1 ] = strides[ d+i ] * sizes[ i ];
}
}
return new x.constructor( getDType( x ), getData( x ), shape, strides, getOffset( x ), ord, { // eslint-disable-line max-len
'readonly': !writable
});
}
// EXPORTS //
module.exports = unflatten;
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