# iterUniqueByHash
> Create an [iterator][mdn-iterator-protocol] which returns unique values according to a hash function.
## Usage
```javascript
var iterUniqueByHash = require( '@stdlib/iter/unique-by-hash' );
```
#### iterUniqueByHash( iterator, hashFcn\[, thisArg] )
Returns an [iterator][mdn-iterator-protocol] which returns unique values according to a hash function.
```javascript
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
## Notes
- A returned [iterator][mdn-iterator-protocol] 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][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.
## Examples
```javascript
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 );
}
```
* * *
## See Also
- [`@stdlib/iter/unique`][@stdlib/iter/unique]: create an iterator which returns unique values.
- [`@stdlib/iter/unique-by`][@stdlib/iter/unique-by]: create an iterator which returns unique values according to a predicate function.
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
[@stdlib/iter/unique]: https://github.com/stdlib-js/iter/tree/main/unique
[@stdlib/iter/unique-by]: https://github.com/stdlib-js/iter/tree/main/unique-by