# iterIntersectionByHash
> Create an [iterator][mdn-iterator-protocol] which returns the intersection of two or more [iterators][mdn-iterator-protocol] according to a hash function.
## Usage
```javascript
var iterIntersectionByHash = require( '@stdlib/iter/intersection-by-hash' );
```
#### iterIntersectionByHash( iter0, ...iterator, hashFcn\[, thisArg] )
Returns an [iterator][mdn-iterator-protocol] which returns the intersection of two or more [iterators][mdn-iterator-protocol] according to a hash function.
```javascript
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
## Notes
- A returned [iterator][mdn-iterator-protocol] 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][mdn-iterator-protocol].
- 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][mdn-iterator-protocol] having **infinite** length.
- If an environment supports `Symbol.iterator` **and** all provided [iterators][mdn-iterator-protocol] are 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 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`][@stdlib/iter/intersection]: create an iterator which returns the intersection of two or more iterators.
- [`@stdlib/iter/unique-by-hash`][@stdlib/iter/unique-by-hash]: create an iterator which returns unique values according to a hash function.
[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
[@stdlib/iter/intersection]: https://github.com/stdlib-js/iter/tree/main/intersection
[@stdlib/iter/unique-by-hash]: https://github.com/stdlib-js/iter/tree/main/unique-by-hash