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iterFilter

Create an iterator which filters the values of another iterator according to a predicate function.

Installation

npm install @stdlib/iter-filter

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var iterFilter = require( '@stdlib/iter-filter' );

iterFilter( iterator, predicate[, thisArg] )

Returns an iterator which filters the values of another iterator according to a predicate function.

var array2iterator = require( '@stdlib/array-to-iterator' );

function predicate( v ) {
    return ( v > 2 );
}

var it = iterFilter( array2iterator( [ 1, 3, 2, 4 ] ), predicate );
// returns <Object>

var v = it.next().value;
// returns 3

v = it.next().value;
// returns 4

var bool = it.next().done;
// returns true

The returned iterator protocol-compliant object has the following properties:

• next: function which returns an iterator 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 is finished.
• return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

The predicate function is provided two arguments:

• value: iterated value.
• index: iteration index (zero-based).

var array2iterator = require( '@stdlib/array-to-iterator' );

function predicate( v, i ) {
    return ( i >= 2 );
}

var it = iterFilter( array2iterator( [ 3, 4, 1, 2 ] ), predicate );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

var bool = it.next().done;
// returns true

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

var array2iterator = require( '@stdlib/array-to-iterator' );

function predicate( v ) {
    this.count += 1;
    return ( v > 0 );
}

var ctx = {
    'count': 0
};

var it = iterFilter( array2iterator( [ 1, 2, 3, 4 ] ), predicate, ctx );
// returns <Object>

var v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

v = it.next().value;
// returns 3

var count = ctx.count;
// returns 3

Notes

• If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var randu = require( '@stdlib/random-iter-randu' );
var iterFilter = require( '@stdlib/iter-filter' );

function predicate( v ) {
    return ( v > 0.5 );
}

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 20
});

// Create an iterator which filters the generated numbers:
var it = iterFilter( rand, predicate );

// Perform manual iteration...
var r;
while ( true ) {
    r = it.next();
    if ( r.done ) {
        break;
    }
    console.log( r.value );
}

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See Also

• @stdlib/iter-filter-map: create an iterator which both filters and maps the values of another iterator.
• @stdlib/iter-map: create an iterator which invokes a function for each iterated value.
• @stdlib/iter-reject: create an iterator which rejects the values of another iterator according to a predicate function.

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Notice

This package is part of 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, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.