npm package: @stdlib/array-base-bifurcate-indices-by
Description: Split element indices into two groups according to a predicate function.
Author: The Stdlib Authors
Latest version: 0.2.3

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# bifurcateIndicesBy

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> Split element indices into two groups according to a predicate function.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-bifurcate-indices-by
```

</section>

<section class="usage">

## Usage

```javascript
var bifurcateIndicesBy = require( '@stdlib/array-base-bifurcate-indices-by' );
```

#### bifurcateIndicesBy( x, predicate\[, thisArg] )

Splits element indices into two groups according to a predicate function.

```javascript
function predicate( v ) {
    return v[ 0 ] === 'b';
}

var x = [ 'beep', 'boop', 'foo', 'bar' ];

var out = bifurcateIndicesBy( x, predicate );
// returns [ [ 0, 1, 3 ], [ 2 ] ]
```

A `predicate` function is provided the following arguments:

-   **value**: current array element.
-   **index**: current array element index.
-   **arr**: input array.

To set the `predicate` function execution context, provide a `thisArg`.

```javascript
function predicate( v ) {
    this.count += 1;
    return v[ 0 ] === 'b';
}

var x = [ 'beep', 'boop', 'foo', 'bar' ];

var context = {
    'count': 0
};
var out = bifurcateIndicesBy( x, predicate, context );
// returns [ [ 0, 1, 3 ], [ 2 ] ]

var cnt = context.count;
// returns 4
```

</section>

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</section>

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<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var take = require( '@stdlib/array-base-take-indexed' );
var bifurcateIndicesBy = require( '@stdlib/array-base-bifurcate-indices-by' );

function predicate( v ) {
    // Use the first letter of each element to define groups:
    return v[ 0 ] === 'b';
}

// 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 [...]

// Split the values:
var out = bifurcateIndicesBy( x, predicate );
// returns [...]

console.log( out );
```

</section>

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* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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