iterIntersectionByHash

Create an iterator which returns the intersection of two or more iterators according to a hash function.

Installation

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

Usage

var iterIntersectionByHash = require( '@stdlib/iter-intersection-by-hash' );

iterIntersectionByHash( iter0, ...iterator, hashFcn[, thisArg] )

Returns an iterator which returns the intersection of two or more iterators according to a hash function.

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

function hashFcn( v ) {
    return v.toString();
}

var it1 = array2iterator( [ 2, 1, 1, 2, 4 ] );
var it2 = array2iterator( [ 3, 4, 3 ] );

var it = iterIntersectionByHash( it1, it2, hashFcn );
// returns <Object>

var 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.

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 values1 = [
    { 'v': 2 },
    { 'v': 1 },
    { 'v': 1 },
    { 'v': 2 }
];
var values2 = [
    { 'v': 4 },
    { 'v': 3 },
    { 'v': 4 },
    { 'v': 3 },
    { 'v': 1 },
    { 'v': 2 }
];

var it1 = array2iterator( values1 );
var it2 = array2iterator( values2 );

var ctx = {
    'count': 0
};

var it = iterIntersectionByHash( it1, it2, hashFcn, ctx );
// returns <Object>

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

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

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

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

Notes

• A returned iterator internally buffers unique hashes, along with the first iterated value resolving to a hash, and, thus, has O(N) memory requirements, where N is the length of the first iterator.
• 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.
• Do not provide iterators having infinite length.
• If an environment supports Symbol.iterator and all provided iterators are iterable, the returned iterator is iterable.

Examples

var discreteUniform = require( '@stdlib/random-iter-discrete-uniform' );
var iterMap = require( '@stdlib/iter-map' );
var iterIntersectionByHash = require( '@stdlib/iter-intersection-by-hash' );

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

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

// Create seeded iterators which can generate 1000 pseudorandom numbers:
var rand1 = discreteUniform( 1, 10, {
    'seed': 1234,
    'iter': 1000
});
var rand2 = discreteUniform( 6, 15, {
    'seed': 1234,
    'iter': 1000
});

// Create iterators which map each number to an object:
var miter1 = iterMap( rand1, mapFcn );
var miter2 = iterMap( rand2, mapFcn );

// Create an iterator which returns the intersection of the above iterators:
var it = iterIntersectionByHash( miter1, miter2, hashFcn );

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

See Also

• @stdlib/iter-intersection: create an iterator which returns the intersection of two or more iterators.
• @stdlib/iter-unique-by-hash: create an iterator which returns unique values according to a hash function.

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

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.