@stdlib/iter-unique-by
TypeScript icon, indicating that this package has built-in type declarations

0.2.1 • Public • Published
About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

iterUniqueBy

NPM version Build Status Coverage Status

Create an iterator which returns unique values according to a predicate function.

Installation

npm install @stdlib/iter-unique-by

Usage

var iterUniqueBy = require( '@stdlib/iter-unique-by' );

iterUniqueBy( iterator, predicate[, thisArg] )

Returns an iterator which returns unique values according to a predicate function.

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

function predicate( a, b ) {
    return ( a !== b );
}

var src = array2iterator( [ 2, 1, 1, 2, 4, 3, 4, 3 ] );

var it = iterUniqueBy( src, predicate );
// returns <Object>

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

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

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

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

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.

A predicate function is provided two arguments:

  • a: a previously identified unique value
  • b: the value whose uniqueness is being determined

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

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

function predicate( a, b ) {
    this.count += 1;
    return ( a.v !== b.v );
}

var values = [
    { 'v': 2 },
    { 'v': 1 },
    { 'v': 1 },
    { 'v': 2 },
    { 'v': 4 },
    { 'v': 3 },
    { 'v': 4 },
    { 'v': 3 }
];

var src = array2iterator( values );

var ctx = {
    'count': 0
};

var it = iterUniqueBy( src, predicate, ctx );
// returns <Object>

var v = it.next().value;
// returns { 'v': 2 }

v = it.next().value;
// returns { 'v': 1 }

v = it.next().value;
// returns { 'v': 4 }

v = it.next().value;
// returns { 'v': 3 }

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

bool = ( ctx.count > 0 );
// returns true

Notes

  • A returned iterator internally buffers unique values and, thus, has O(N) memory requirements.
  • A predicate function is invoked for each iterated value against each value in an internal buffer consisting of previously identified unique values. Thus, as the number of unique values grows, so, too, does the number of predicate function invocations per iterated value.
  • An iterated value is considered "unique" if the predicate function returns truthy values for all comparisons of the iterated value with each value in the internal buffer.
  • If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var discreteUniform = require( '@stdlib/random-iter-discrete-uniform' );
var iterUniqueBy = require( '@stdlib/iter-unique-by' );

function predicate( a, b ) {
    return ( a !== b );
}

// Create a seeded iterator which can generate 1000 pseudorandom numbers:
var rand = discreteUniform( 1, 10, {
    'seed': 1234,
    'iter': 1000
});

// Create an iterator which returns unique values:
var it = iterUniqueBy( rand, predicate );

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

See Also


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

Chat


License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.

Package Sidebar

Install

npm i @stdlib/iter-unique-by

Homepage

stdlib.io

Weekly Downloads

13

Version

0.2.1

License

Apache-2.0

Unpacked Size

39.7 kB

Total Files

11

Last publish

Collaborators

  • stdlib-bot
  • kgryte
  • planeshifter
  • rreusser