# IndexSet A collection of unique integer values that represent the indexes of elements in another collection. ``` struct IndexSet ``` ## Overview The range of valid integer values is `0...Int.max-1`. Anything outside this range is an error. ## Topics ### Creating an Index Set [`init()`](/documentation/Foundation/IndexSet/init()) Initializes an empty index set. [`init(integer:)`](/documentation/Foundation/IndexSet/init(integer:)) Initializes an index set with a single integer. [`init(integersIn:)`](/documentation/Foundation/IndexSet/init(integersIn:)-40cz3) Initializes an index set with a range of integers. ### Counting Items in a Set [`count(in:)`](/documentation/Foundation/IndexSet/count(in:)-v622) Returns the count of integers in `self` that intersect `range`. ### Accessing Elements [`subscript(_:)`](/documentation/Foundation/IndexSet/subscript(_:)) Accesses one element in the index set. ### Combining Index Sets [`formIntersection(_:)`](/documentation/Foundation/IndexSet/formIntersection(_:)) Intersects the `IndexSet` with `other`. [`formSymmetricDifference(_:)`](/documentation/Foundation/IndexSet/formSymmetricDifference(_:)) Exclusive or the `IndexSet` with `other`. [`formUnion(_:)`](/documentation/Foundation/IndexSet/formUnion(_:)) Union the `IndexSet` with `other`. [`intersection(_:)`](/documentation/Foundation/IndexSet/intersection(_:)) Intersects the `IndexSet` with `other`. [`symmetricDifference(_:)`](/documentation/Foundation/IndexSet/symmetricDifference(_:)) Exclusive or the `IndexSet` with `other`. [`union(_:)`](/documentation/Foundation/IndexSet/union(_:)) Union the `IndexSet` with `other`. ### Inserting Elements [`insert(_:)`](/documentation/Foundation/IndexSet/insert(_:)) Insert an integer into the `IndexSet`. [`insert(integersIn:)`](/documentation/Foundation/IndexSet/insert(integersIn:)-28eld) Insert a range of integers into the `IndexSet`. [`update(with:)`](/documentation/Foundation/IndexSet/update(with:)) Insert an integer into the `IndexSet`. ### Removing Elements [`remove(_:)`](/documentation/Foundation/IndexSet/remove(_:)) Remove an integer from the `IndexSet`. [`remove(integersIn:)`](/documentation/Foundation/IndexSet/remove(integersIn:)-7dhfw) Remove a range of integers from the `IndexSet`. [`remove(integersIn:)`](/documentation/Foundation/IndexSet/remove(integersIn:)-54370) Remove a range of integers from the `IndexSet`. [`removeAll()`](/documentation/Foundation/IndexSet/removeAll()) Remove all values from the `IndexSet`. ### Testing Set Membership [`contains(_:)`](/documentation/Foundation/IndexSet/contains(_:)) Returns `true` if `self` contains `integer`. [`contains(integersIn:)`](/documentation/Foundation/IndexSet/contains(integersIn:)-9frtv) Returns `true` if `self` contains all of the integers in `indexSet`. [`contains(integersIn:)`](/documentation/Foundation/IndexSet/contains(integersIn:)-sma8) Returns `true` if `self` contains all of the integers in `range`. [`intersects(integersIn:)`](/documentation/Foundation/IndexSet/intersects(integersIn:)-3sdmv) Returns `true` if `self` intersects any of the integers in `range`. ### Manipulating Indexes [`startIndex`](/documentation/Foundation/IndexSet/startIndex) The beginning index in the set. [`endIndex`](/documentation/Foundation/IndexSet/endIndex) The ending index in the set. [`index(after:)`](/documentation/Foundation/IndexSet/index(after:)) Returns the index that follows the given index in the set. [`index(before:)`](/documentation/Foundation/IndexSet/index(before:)) Returns the index that precedes the given index in the set. [`formIndex(after:)`](/documentation/Foundation/IndexSet/formIndex(after:)) Modifies the given index to refer to the item after the one it currently refers to. [`formIndex(before:)`](/documentation/Foundation/IndexSet/formIndex(before:)) Modifies the given index to refer to the item before the one it currently refers to. [`indexRange(in:)`](/documentation/Foundation/IndexSet/indexRange(in:)-539lz) Return a `Range` which can be used to subscript the index set. ### Finding Elements [`integerLessThanOrEqualTo(_:)`](/documentation/Foundation/IndexSet/integerLessThanOrEqualTo(_:)) Returns an integer contained in `self` which is less than or equal to `integer`, or `nil` if a result could not be found. [`integerGreaterThan(_:)`](/documentation/Foundation/IndexSet/integerGreaterThan(_:)) Returns an integer contained in `self` which is greater than `integer`, or `nil` if a result could not be found. [`integerGreaterThanOrEqualTo(_:)`](/documentation/Foundation/IndexSet/integerGreaterThanOrEqualTo(_:)) Returns an integer contained in `self` which is greater than or equal to `integer`, or `nil` if a result could not be found. [`integerLessThan(_:)`](/documentation/Foundation/IndexSet/integerLessThan(_:)) Returns an integer contained in `self` which is less than `integer`, or `nil` if a result could not be found. ### Selecting Elements [`filteredIndexSet(in:includeInteger:)`](/documentation/Foundation/IndexSet/filteredIndexSet(in:includeInteger:)-6cdvc) Returns an IndexSet filtered according to the result of `includeInteger`. [`filteredIndexSet(in:includeInteger:)`](/documentation/Foundation/IndexSet/filteredIndexSet(in:includeInteger:)-9dn86) Returns an IndexSet filtered according to the result of `includeInteger`. [`filteredIndexSet(includeInteger:)`](/documentation/Foundation/IndexSet/filteredIndexSet(includeInteger:)) Returns an IndexSet filtered according to the result of `includeInteger`. ### Excluding Elements ### Transforming Elements ### Iterating Over Elements [`makeIterator()`](/documentation/Foundation/IndexSet/makeIterator()) Returns an iterator over the elements of this sequence. ### Sorting Elements ### Shifting Index Groups [`shift(startingAt:by:)`](/documentation/Foundation/IndexSet/shift(startingAt:by:)) For a positive delta, shifts the indexes in [index, INT_MAX] to the right, thereby inserting an “empty space” [index, delta], for a negative delta, shifts the indexes in [index, INT_MAX] to the left, thereby deleting the indexes in the range [index - delta, delta]. ### Splitting the Set ### Getting a Range-Based View [`rangeView(of:)`](/documentation/Foundation/IndexSet/rangeView(of:)-5xqe8) Returns a `Range`-based view of `self`. [`rangeView`](/documentation/Foundation/IndexSet/rangeView-swift.property) Returns a `Range`-based view of the entire contents of `self`. [`IndexSet.RangeView`](/documentation/Foundation/IndexSet/RangeView-swift.struct) A view of the contents of an IndexSet, organized by range. ### Using Reference Types [`NSIndexSet`](/documentation/Foundation/NSIndexSet) An immutable collection of unique integer values that represent indexes in another collection. [`NSMutableIndexSet`](/documentation/Foundation/NSMutableIndexSet) A mutable collection of unique integer values that represent indexes in another collection. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)