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# BoxSetRetainAll

Retain only the elements of a Set that are also present in the given collection, removing everything else.

This is the in-place equivalent of computing an intersection. The Set is modified in place and returned to support method chaining.

## Method Signature

```
BoxSetRetainAll(set=[modifiableSet], values=[any])
```

### Arguments

| Argument | Type            | Required | Description                                                                                                                                             | Default |
| -------- | --------------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------- | ------- |
| `set`    | `modifiableSet` | `true`   | The set to filter in place.                                                                                                                             |         |
| `values` | `any`           | `true`   | <p>The collection whose membership determines which elements are kept. Accepts an Array, Set,<br>list-delimited String, or any castable collection.</p> |         |

## Examples

### Keep only elements that are also in another collection

Elements NOT present in the argument collection are removed.

```java
s = [ 1, 2, 3, 4, 5 ].toSet();
s.retainAll( [ 3, 4, 999 ] );
writeOutput( s.size() );

```

Result: 2

### Intersect a Set in-place

```java
a = setOf( "a", "b", "c", "d" );
a.retainAll( [ "b", "d" ] );
writeOutput( a.size() );

```

Result: 2

## Related

* [BoxSetAdd](/boxlang-language/reference/built-in-functions/set/boxsetadd.md)
* [BoxSetAddAll](/boxlang-language/reference/built-in-functions/set/boxsetaddall.md)
* [BoxSetClear](/boxlang-language/reference/built-in-functions/set/boxsetclear.md)
* [BoxSetContains](/boxlang-language/reference/built-in-functions/set/boxsetcontains.md)
* [BoxSetContainsAll](/boxlang-language/reference/built-in-functions/set/boxsetcontainsall.md)
* [BoxSetDifference](/boxlang-language/reference/built-in-functions/set/boxsetdifference.md)
* [BoxSetEach](/boxlang-language/reference/built-in-functions/set/boxseteach.md)
* [BoxSetEquals](/boxlang-language/reference/built-in-functions/set/boxsetequals.md)
* [BoxSetEvery](/boxlang-language/reference/built-in-functions/set/boxsetevery.md)
* [BoxSetFilter](/boxlang-language/reference/built-in-functions/set/boxsetfilter.md)
* [BoxSetFind](/boxlang-language/reference/built-in-functions/set/boxsetfind.md)
* [BoxSetIntersection](/boxlang-language/reference/built-in-functions/set/boxsetintersection.md)
* [BoxSetIsDisjointFrom](/boxlang-language/reference/built-in-functions/set/boxsetisdisjointfrom.md)
* [BoxSetIsEmpty](/boxlang-language/reference/built-in-functions/set/boxsetisempty.md)
* [BoxSetIsSubsetOf](/boxlang-language/reference/built-in-functions/set/boxsetissubsetof.md)
* [BoxSetIsSupersetOf](/boxlang-language/reference/built-in-functions/set/boxsetissupersetof.md)
* [BoxSetMap](/boxlang-language/reference/built-in-functions/set/boxsetmap.md)
* [BoxSetNone](/boxlang-language/reference/built-in-functions/set/boxsetnone.md)
* [BoxSetReduce](/boxlang-language/reference/built-in-functions/set/boxsetreduce.md)
* [BoxSetReject](/boxlang-language/reference/built-in-functions/set/boxsetreject.md)
* [BoxSetRemove](/boxlang-language/reference/built-in-functions/set/boxsetremove.md)
* [BoxSetRemoveAll](/boxlang-language/reference/built-in-functions/set/boxsetremoveall.md)
* [BoxSetSome](/boxlang-language/reference/built-in-functions/set/boxsetsome.md)
* [BoxSetSymmetricDifference](/boxlang-language/reference/built-in-functions/set/boxsetsymmetricdifference.md)
* [BoxSetToArray](/boxlang-language/reference/built-in-functions/set/boxsettoarray.md)
* [BoxSetToList](/boxlang-language/reference/built-in-functions/set/boxsettolist.md)
* [BoxSetUnion](/boxlang-language/reference/built-in-functions/set/boxsetunion.md)
* [ObjectToSet](/boxlang-language/reference/built-in-functions/set/objecttoset.md)
* [SetNew](/boxlang-language/reference/built-in-functions/set/setnew.md)
* [SetOf](/boxlang-language/reference/built-in-functions/set/setof.md)
* [StructKeySet](/boxlang-language/reference/built-in-functions/set/structkeyset.md)
* [StructValueSet](/boxlang-language/reference/built-in-functions/set/structvalueset.md)


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