@stdlib/iter-unique-by-hash

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

Usage no npm install needed!

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README

iterUniqueByHash

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

Installation

npm install @stdlib/iter-unique-by-hash

Usage

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

iterUniqueByHash( iterator, hashFcn[, thisArg] )

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

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

function hashFcn( v ) {
    return v;
}

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

var it = iterUniqueByHash( src, hashFcn );
// 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 hash function is provided one argument:

  • v: the current iterated value

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

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

function hashFcn( v ) {
    this.count += 1;
    return JSON.stringify( 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 = iterUniqueByHash( src, hashFcn, 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 hashes and, thus, has O(N) memory requirements.
  • An iterated value is considered "unique" if a hash function returns a unique hash value for that iterated value. Beware that this may result in unexpected behavior. Namely, only the first iterated value mapping to a particular hash function result is returned, even if subsequent values, while mapping to the same hash, are different. Accordingly, iteration order does matter.
  • 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 iterMap = require( '@stdlib/iter-map' );
var iterUniqueByHash = require( '@stdlib/iter-unique-by-hash' );

function mapFcn( v ) {
    return {
        'v': v
    };
}

function hashFcn( v ) {
    return JSON.stringify( v );
}

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

// Create an iterator which maps each number to an object:
var miter = iterMap( rand, mapFcn );

// Create an iterator which returns unique (object) values:
var it = iterUniqueByHash( miter, hashFcn );

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

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.

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License

See LICENSE.

Copyright

Copyright © 2016-2021. The Stdlib Authors.