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base/group-indices-by/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.
+
+-->
+
+# groupIndicesBy
+
+> Group element indices according to an indicator function.
+
+<!-- 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 groupIndicesBy = require( '@stdlib/array/base/group-indices-by' );
+```
+
+#### groupIndicesBy( x, indicator\[, thisArg] )
+
+Groups element indices according to an indicator function.
+
+```javascript
+function indicator( v ) {
+    return v[ 0 ];
+}
+
+var x = [ 'beep', 'boop', 'foo', 'bar' ];
+
+var out = groupIndicesBy( x, indicator );
+// returns { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }
+```
+
+An `indicator` function is provided the following arguments:
+
+-   **value**: current array element.
+-   **index**: current array element index.
+-   **arr**: input array.
+
+To set the `indicator` function execution context, provide a `thisArg`.
+
+```javascript
+function indicator( v ) {
+    this.count += 1;
+    return v[ 0 ];
+}
+
+var x = [ 'beep', 'boop', 'foo', 'bar' ];
+
+var context = {
+    'count': 0
+};
+var out = groupIndicesBy( x, indicator, context );
+// returns { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }
+
+var cnt = context.count;
+// returns 4
+```
+
+</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 value returned by an `indicator` function should be a value which can be serialized as an object key. As a counterexample,
+
+    ```javascript
+    function indicator( v ) {
+        return {};
+    }
+    var x = [ 'beep', 'boop', 'foo', 'bar' ];
+
+    var out = groupIndicesBy( x, indicator );
+    // returns { '[object Object]': [ 0, 1, 2, 3 ] }
+    ```
+
+    while each group identifier is unique, all input array elements resolve to the same group because each group identifier serializes to the same string.
+
+</section>
+
+<!-- /.notes -->
+
+<!-- Package usage examples. -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
+var take = require( '@stdlib/array/base/take' );
+var groupIndicesBy = require( '@stdlib/array/base/group-indices-by' );
+
+function indicator( v ) {
+    // Use the first letter of each element to define groups:
+    return v[ 0 ];
+}
+
+// Define an initial array of values:
+var values = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ];
+
+// Sample from the initial array to generate a random collection:
+var indices = discreteUniform( 100, 0, values.length-1, {
+    'dtype': 'generic'
+});
+var x = take( values, indices );
+// returns [...]
+
+// Group the values:
+var out = groupIndicesBy( x, indicator );
+// returns {...}
+
+console.log( 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 -->

base/group-indices-by/benchmark/benchmark.length.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 pow = require( '@stdlib/math/base/special/pow' );
+var isPlainObject = require( '@stdlib/assert/is-plain-object' );
+var zeroTo = require( './../../../base/zero-to' );
+var pkg = require( './../package.json' ).name;
+var groupIndicesBy = require( './../lib' );
+
+
+// FUNCTIONS //
+
+/**
+* Indicator function.
+*
+* @private
+* @param {*} value - current array element
+* @param {NonNegativeInteger} index - current array element index
+* @param {Collection} arr - input array
+* @returns {*} indicator value
+*/
+function indicator( value, index ) {
+	return index; // note: this corresponds to the extreme case where every element is in a distinct group
+}
+
+/**
+* Creates a benchmark function.
+*
+* @private
+* @param {PositiveInteger} len - array length
+* @returns {Function} benchmark function
+*/
+function createBenchmark( len ) {
+	var x = zeroTo( len );
+	return benchmark;
+
+	/**
+	* Benchmark function.
+	*
+	* @private
+	* @param {Benchmark} b - benchmark instance
+	*/
+	function benchmark( b ) {
+		var out;
+		var i;
+
+		b.tic();
+		for ( i = 0; i < b.iterations; i++ ) {
+			out = groupIndicesBy( x, indicator );
+			if ( typeof out !== 'object' ) {
+				b.fail( 'should return an object' );
+			}
+		}
+		b.toc();
+		if ( !isPlainObject( out ) ) {
+			b.fail( 'should return an object' );
+		}
+		b.pass( 'benchmark finished' );
+		b.end();
+	}
+}
+
+
+// MAIN //
+
+/**
+* Main execution sequence.
+*
+* @private
+*/
+function main() {
+	var len;
+	var min;
+	var max;
+	var f;
+	var i;
+
+	min = 1; // 10^min
+	max = 6; // 10^max
+
+	for ( i = min; i <= max; i++ ) {
+		len = pow( 10, i );
+
+		f = createBenchmark( len );
+		bench( pkg+':len='+len+',num_groups='+len, f );
+	}
+}
+
+main();

base/group-indices-by/docs/repl.txt

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+
+{{alias}}( x, indicator[, thisArg] )
+    Groups element indices according to an indicator function.
+
+    When invoked, the indicator function is provided the following arguments:
+
+    - value: current array element.
+    - index: current array element index.
+    - arr: input array.
+
+    The value returned by an indicator function should be a value which can be
+    serialized as an object key.
+
+    If provided an empty array, the function returns an empty object.
+
+    Parameters
+    ----------
+    x: ArrayLike
+        Input array.
+
+    indicator: Function
+        Indicator function specifying which group an element in the input array
+        belongs to.
+
+    thisArg: any (optional)
+        Indicator function execution context.
+
+    Returns
+    -------
+    out: Object
+        Group results.
+
+    Examples
+    --------
+    > function fcn( v ) { return v[ 0 ]; };
+    > var x = [ 'beep', 'boop', 'foo', 'bar' ];
+    > var out = {{alias}}( x, fcn )
+    { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }
+
+    See Also
+    --------
+