feat: add array/base/flatten-by

Author: kgryte

lib/node_modules/@stdlib/array/base/flatten-by/README.md

@@ -0,0 +1,213 @@
+<!--
+
+@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.
+
+-->
+
+<!-- lint disable maximum-heading-length -->
+
+# flattenBy
+
+> Flatten an n-dimensional nested array according to a callback function.
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var flattenBy = require( '@stdlib/array/base/flatten-by' );
+```
+
+#### flattenBy( x, shape, colexicographic, clbk\[, thisArg] )
+
+Flattens an n-dimensional nested array according to a callback function.
+
+```javascript
+function scale( v ) {
+    return v * 2;
+}
+
+var x = [ [ 1, 2 ], [ 3, 4 ] ];
+
+var out = flattenBy( x, [ 2, 2 ], false, scale );
+// returns [ 2, 4, 6, 8 ]
+```
+
+To flatten in colexicographic order, provide a third argument equal to `true`.
+
+```javascript
+function scale( v ) {
+    return v * 2;
+}
+
+var x = [ [ 1, 2 ], [ 3, 4 ] ];
+
+var out = flattenBy( x, [ 2, 2 ], true, scale );
+// returns [ 2, 6, 4, 8 ]
+```
+
+To set the callback execution context, provide a `thisArg` argument.
+
+<!-- eslint-disable no-invalid-this -->
+
+```javascript
+function scale( v ) {
+    this.count += 1;
+    return v * 2;
+}
+
+var x = [ [ 1, 2 ], [ 3, 4 ] ];
+var ctx = {
+    'count': 0
+};
+
+var out = flattenBy( x, [ 2, 2 ], false, scale, ctx );
+// returns [ 2, 4, 6, 8 ]
+
+var count = ctx.count;
+// returns 4
+```
+
+#### flattenBy.assign( x, shape, colexicographic, out, stride, offset, clbk\[, thisArg] )
+
+Flattens an n-dimensional nested array according to a callback function and assigns elements to a provided output array.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+function scale( v ) {
+    return v * 2;
+}
+
+var x = [ [ 1, 2 ], [ 3, 4 ] ];
+var out = new Float64Array( 4 );
+
+var y = flattenBy.assign( x, [ 2, 2 ], false, out, 1, 0, scale );
+// returns <Float64Array>[ 2, 4, 6, 8 ]
+
+var bool = ( y === out );
+// returns true
+
+y = flattenBy.assign( x, [ 2, 2 ], true, out, 1, 0, scale );
+// returns <Float64Array>[ 2, 6, 4, 8 ]
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   A callback function is provided the following arguments:
+
+    -   **value**: nested array element.
+    -   **indices**: element indices (in lexicographic order).
+    -   **arr**: the input array.
+
+-   Both functions assume that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var naryFunction = require( '@stdlib/utils/nary-function' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var flattenBy = require( '@stdlib/array/base/flatten-by' );
+
+var fcn = naryFunction( abs, 1 );
+
+// Define a 2x2x1x2x2 array:
+var x = [
+    [
+        [
+            [
+                [ -1, -2 ], [ -3, -4 ]
+            ]
+        ],
+        [
+            [
+                [ -5, -6 ], [ -7, -8 ]
+            ]
+        ]
+    ],
+    [
+        [
+            [
+                [ -9, -10 ], [ -11, -12 ]
+            ]
+        ],
+        [
+            [
+                [ -13, -14 ], [ -15, -16 ]
+            ]
+        ]
+    ]
+];
+
+var out = flattenBy( x, [ 0, 0, 0, 0, 0 ], false, fcn );
+// returns []
+
+out = flattenBy( x, [ 0, 0, 0, 0, 0 ], true, fcn );
+// returns []
+
+out = flattenBy( x, [ 1, 1, 1, 1, 1 ], false, fcn );
+// returns [ 1 ]
+
+out = flattenBy( x, [ 1, 1, 1, 1, 1 ], true, fcn );
+// returns [ 1 ]
+
+out = flattenBy( x, [ 1, 2, 1, 2, 2 ], false, fcn );
+// returns [ 1, 2, 3, 4, 5, 6, 7, 8 ]
+
+out = flattenBy( x, [ 1, 2, 1, 2, 2 ], true, fcn );
+// returns [ 1, 5, 3, 7, 2, 6, 4, 8 ]
+
+out = flattenBy( x, [ 2, 2, 1, 2, 2 ], false, fcn );
+// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ]
+
+out = flattenBy( x, [ 2, 2, 1, 2, 2 ], true, fcn );
+// returns [ 1, 9, 5, 13, 3, 11, 7, 15, 2, 10, 6, 14, 4, 12, 8, 16 ]
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- 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 -->