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iter/column-entries/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2023 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.
+
+-->
+
+# nditerColumnEntries
+
+> Create an iterator which returns `[index, column]` pairs for each column in a matrix (or stack of matrices).
+
+<!-- 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 nditerColumnEntries = require( '@stdlib/ndarray/iter/column-entries' );
+```
+
+#### nditerColumnEntries( x\[, options] )
+
+Returns an iterator which returns `[index, column]` pairs for each column in a matrix (or stack of matrices).
+
+```javascript
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+var array = require( '@stdlib/ndarray/array' );
+
+var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
+// returns <ndarray>
+
+var iter = nditerColumnEntries( x );
+
+var v = iter.next().value;
+// returns [...]
+
+var idx = v[ 0 ];
+// returns [ 0, null, 0 ]
+
+var col = ndarray2array( v[ 1 ] );
+// returns [ 1, 3 ]
+
+v = iter.next().value;
+// returns [...]
+
+idx = v[ 0 ];
+// returns [ 0, null, 1 ]
+
+col = ndarray2array( v[ 1 ] );
+// returns [ 2, 4 ]
+
+// ...
+```
+
+The function accepts the following `options`:
+
+-   **readonly**: boolean indicating whether returned [`ndarray`][@stdlib/ndarray/ctor] views should be read-only. In order to return writable [`ndarray`][@stdlib/ndarray/ctor] views, the input [`ndarray`][@stdlib/ndarray/ctor] must be writable. If the input [`ndarray`][@stdlib/ndarray/ctor] is read-only, setting this option to `false` raises an exception. Default: `true`.
+
+By default, the iterator returns [`ndarray`][@stdlib/ndarray/ctor] views which are **read-only**. To return writable [views][@stdlib/ndarray/slice], set the `readonly` option to `false`.
+
+```javascript
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+var array = require( '@stdlib/ndarray/array' );
+
+var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
+// returns <ndarray>
+
+var iter = nditerColumnEntries( x, {
+    'readonly': false
+});
+
+var v = iter.next().value;
+// returns [...]
+
+var col = ndarray2array( v[ 1 ] );
+// returns [ 1, 3 ]
+
+v[ 1 ].set( 0, 10 );
+
+col = ndarray2array( v[ 1 ] );
+// returns [ 10, 3 ]
+```
+
+The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties:
+
+-   **next**: function which returns an [iterator][mdn-iterator-protocol] protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the [iterator][mdn-iterator-protocol] is finished.
+-   **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object.
+
+</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
+
+-   Each returned index is a Cartesian index (i.e., an array of subscripts/dimension indices). A dimension index equal to `null` indicates that all values along the respective dimension are included in the returned [`ndarray`][@stdlib/ndarray/ctor].
+-   If an environment supports `Symbol.iterator`, the returned iterator is iterable.
+-   A returned iterator does **not** copy a provided [`ndarray`][@stdlib/ndarray/ctor]. To ensure iterable reproducibility, copy the input [`ndarray`][@stdlib/ndarray/ctor] **before** creating an iterator. Otherwise, any changes to the contents of input [`ndarray`][@stdlib/ndarray/ctor] will be reflected in the returned iterator.
+-   In environments supporting `Symbol.iterator`, the function **explicitly** does **not** invoke an ndarray's `@@iterator` method, regardless of whether this method is defined.
+
+</section>
+
+<!-- /.notes -->
+
+<!-- Package usage examples. -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+var array = require( '@stdlib/ndarray/array' );
+var zeroTo = require( '@stdlib/array/base/zero-to' );
+var nditerColumnEntries = require( '@stdlib/ndarray/iter/column-entries' );
+
+// Define an input array:
+var x = array( zeroTo( 27 ), {
+    'shape': [ 3, 3, 3 ]
+});
+
+// Create an iterator for returning [index, column] pairs:
+var it = nditerColumnEntries( x );
+
+// Perform manual iteration...
+var v;
+while ( true ) {
+    v = it.next();
+    if ( v.done ) {
+        break;
+    }
+    console.log( v.value[ 0 ] );
+    console.log( ndarray2array( v.value[ 1 ] ) );
+}
+```
+
+</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">
+
+[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
+
+[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor
+
+[@stdlib/ndarray/slice]: https://github.com/stdlib-js/ndarray/tree/main/slice
+
+</section>
+
+<!-- /.links -->

iter/column-entries/benchmark/benchmark.js

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+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 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 isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
+var isArray = require( '@stdlib/assert/is-array' );
+var array = require( './../../../array' );
+var zeros = require( './../../../zeros' );
+var pkg = require( './../package.json' ).name;
+var nditerColumnEntries = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg, function benchmark( b ) {
+	var iter;
+	var x;
+	var i;
+
+	x = array( [ [ [ 1, 2, 3, 4 ] ] ] );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		iter = nditerColumnEntries( x );
+		if ( typeof iter !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !isIteratorLike( iter ) ) {
+		b.fail( 'should return an iterator protocol-compliant object' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( pkg+'::iteration', function benchmark( b ) {
+	var iter;
+	var x;
+	var z;
+	var i;
+
+	x = zeros( [ b.iterations+1, 1, 1 ], {
+		'dtype': 'generic'
+	});
+
+	iter = nditerColumnEntries( x );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		z = iter.next().value;
+		if ( typeof z !== 'object' ) {
+			b.fail( 'should return an array' );
+		}
+	}
+	b.toc();
+	if ( !isArray( z ) ) {
+		b.fail( 'should return an array' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});

iter/column-entries/docs/repl.txt

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+
+{{alias}}( x[, options] )
+    Returns an iterator which returns [index, column] pairs for each column in a
+    matrix (or stack of matrices).
+
+    Each returned index is a Cartesian index (i.e., an array of subscripts/
+    dimension indices). A dimension index equal to `null` indicates that all
+    values along the respective dimension are included in the returned ndarray.
+
+    If an environment supports Symbol.iterator, the returned iterator is
+    iterable.
+
+    If an environment supports Symbol.iterator, the function explicitly does not
+    invoke an ndarray's `@@iterator` method, regardless of whether this method
+    is defined.
+
+    Parameters
+    ----------
+    x: ndarray
+        Input array.
+
+    options: Object (optional)
+        Options.
+
+    options.readonly: boolean (optional)
+        Boolean indicating whether returned ndarray views should be read-only.
+        If the input ndarray is read-only, setting this option to `false` raises
+        an exception. Default: true.
+
+    Returns
+    -------
+    iterator: Object
+        Iterator.
+
+    iterator.next(): Function
+        Returns an iterator protocol-compliant object containing the next
+        iterated value (if one exists) and a boolean flag indicating whether the
+        iterator is finished.
+
+    iterator.return( [value] ): Function
+        Finishes an iterator and returns a provided value.
+
+    Examples
+    --------
+    > var x = {{alias:@stdlib/ndarray/array}}( [ [ 1, 2 ], [ 3, 4 ] ] );
+    > var it = {{alias}}( x );
+    > var v = it.next().value;
+    > v[ 0 ]
+    [ null, 0 ]
+    > {{alias:@stdlib/ndarray/to-array}}( v[ 1 ] )
+    [ 1, 3 ]
+    > v = it.next().value;
+    > v[ 0 ]
+    [ null, 1 ]
+    > {{alias:@stdlib/ndarray/to-array}}( v[ 1 ] )
+    [ 2, 4 ]
+
+    See Also
+    --------
+