@stdlib/iter-unique-by
v0.2.2
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Create an iterator which returns unique values according to a predicate function.
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iterUniqueBy
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 adone
property having aboolean
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 ofpredicate
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
@stdlib/iter-unique
: create an iterator which returns unique values.@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.