feat: add ndarray/base/unflatten

lib/node_modules/@stdlib/ndarray/base/unflatten/README.md

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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.
+
+-->
+
+# unflatten
+
+> Return a view of an input ndarray in which a specified dimension is expanded over multiple dimensions.
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<!-- Package usage documentation. -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var unflatten = require( '@stdlib/ndarray/base/unflatten' );
+```
+
+#### unflatten( x, dim, sizes, writable )
+
+Returns a view of an input ndarray in which a specified dimension is expanded over multiple dimensions.
+
+```javascript
+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 ] ]
+```
+
+The function accepts the following arguments:
+
+-   **x**: input ndarray.
+-   **dim**: dimension to be unflattened. If provided an integer less than zero, the dimension index is resolved relative to the last dimension, with the last dimension corresponding to the value `-1`.
+-   **sizes**: new shape of the unflattened dimension.
+-   **writable**: boolean indicating whether a returned ndarray should be writable.
+
+</section>
+
+<!-- /.usage -->
+
+<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+## Notes
+
+-   The `writable` parameter **only** applies to ndarray constructors supporting **read-only** instances.
+
+</section>
+
+<!-- /.notes -->
+
+<!-- Package usage examples. -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var uniform = require( '@stdlib/random/discrete-uniform' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+var unflatten = require( '@stdlib/ndarray/base/unflatten' );
+
+var x = uniform( [ 12 ], -100, 100 );
+console.log( ndarray2array( x ) );
+
+var out = unflatten( x, 0, [ 3, 4 ], false );
+console.log( ndarray2array( out ) );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="references">
+
+</section>
+
+<!-- /.references -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/ndarray/base/unflatten/benchmark/benchmark.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 bench = require( '@stdlib/bench' );
+var Float64Array = require( '@stdlib/array/float64' );
+var ndarrayBase = require( '@stdlib/ndarray/base/ctor' );
+var ndarray = require( '@stdlib/ndarray/ctor' );
+var isndarrayLike = require( '@stdlib/assert/is-ndarray-like' );
+var format = require( '@stdlib/string/format' );
+var pkg = require( './../package.json' ).name;
+var unflatten = require( './../lib' );
+
+
+// MAIN //
+
+bench( format( '%s::base_ndarray, 2d, row-major', pkg ), function benchmark( b ) {
+	var strides;
+	var values;
+	var buffer;
+	var offset;
+	var dtype;
+	var shape;
+	var order;
+	var sizes;
+	var out;
+	var i;
+
+	dtype = 'float64';
+	buffer = new Float64Array( 24 );
+	shape = [ 2, 12 ];
+	strides = [ 12, 1 ];
+	offset = 0;
+	order = 'row-major';
+	sizes = [ 3, 4 ];
+
+	values = [
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order )
+	];
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		out = unflatten( values[ i%values.length ], 1, sizes, false );
+		if ( typeof out !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !isndarrayLike( out ) ) {
+		b.fail( 'should return an ndarray' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( format( '%s::ndarray, 2d, row-major', pkg ), function benchmark( b ) {
+	var strides;
+	var values;
+	var buffer;
+	var offset;
+	var dtype;
+	var shape;
+	var order;
+	var sizes;
+	var out;
+	var i;
+
+	dtype = 'float64';
+	buffer = new Float64Array( 24 );
+	shape = [ 2, 12 ];
+	strides = [ 12, 1 ];
+	offset = 0;
+	order = 'row-major';
+	sizes = [ 3, 4 ];
+
+	values = [
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order )
+	];
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		out = unflatten( values[ i%values.length ], 1, sizes, false );
+		if ( typeof out !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !isndarrayLike( out ) ) {
+		b.fail( 'should return an ndarray' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( format( '%s::base_ndarray, 2d, column-major', pkg ), function benchmark( b ) {
+	var strides;
+	var values;
+	var buffer;
+	var offset;
+	var dtype;
+	var shape;
+	var order;
+	var sizes;
+	var out;
+	var i;
+
+	dtype = 'float64';
+	buffer = new Float64Array( 24 );
+	shape = [ 2, 12 ];
+	strides = [ 1, 2 ];
+	offset = 0;
+	order = 'column-major';
+	sizes = [ 3, 4 ];
+
+	values = [
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order ),
+		ndarrayBase( dtype, buffer, shape, strides, offset, order )
+	];
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		out = unflatten( values[ i%values.length ], 1, sizes, false );
+		if ( typeof out !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !isndarrayLike( out ) ) {
+		b.fail( 'should return an ndarray' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( format( '%s::ndarray, 2d, column-major', pkg ), function benchmark( b ) {
+	var strides;
+	var values;
+	var buffer;
+	var offset;
+	var dtype;
+	var shape;
+	var order;
+	var sizes;
+	var out;
+	var i;
+
+	dtype = 'float64';
+	buffer = new Float64Array( 24 );
+	shape = [ 2, 12 ];
+	strides = [ 1, 2 ];
+	offset = 0;
+	order = 'column-major';
+	sizes = [ 3, 4 ];
+
+	values = [
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order ),
+		ndarray( dtype, buffer, shape, strides, offset, order )
+	];
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		out = unflatten( values[ i%values.length ], 1, sizes, false );
+		if ( typeof out !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !isndarrayLike( out ) ) {
+		b.fail( 'should return an ndarray' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});

lib/node_modules/@stdlib/ndarray/base/unflatten/docs/repl.txt

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+
+{{alias}}( x, dim, sizes, writable )
+    Returns a view of an input ndarray in which a specified dimension is
+    expanded over multiple dimensions.
+
+    Parameters
+    ----------
+    x: ndarray
+        Input array.
+
+    dim: integer
+        Dimension to be unflattened. If provided an integer less than zero,
+        the dimension index is resolved relative to the last dimension, with
+        the last dimension corresponding to the value `-1`.
+
+    sizes: ArrayLikeObject<NonNegativeInteger>
+        New shape of the unflattened dimension.
+
+    writable: boolean
+        Boolean indicating whether the returned ndarray should be writable.
+
+    Returns
+    -------
+    out: ndarray
+        Output array.
+
+    Examples
+    --------
+    > var x = {{alias:@stdlib/ndarray/array}}( [ 1, 2, 3, 4, 5, 6 ] )
+    <ndarray>[ 1, 2, 3, 4, 5, 6 ]
+    > var out = {{alias}}( x, 0, [ 2, 3 ], false )
+    <ndarray>[ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
+
+    See Also
+    --------