# prefix(_:) Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection. ``` func prefix(_ maxLength: Int) -> Self.SubSequence ``` ## Parameters `maxLength` The maximum number of elements to return. `maxLength` must be greater than or equal to zero. ## Return Value A subsequence starting at the beginning of this collection with at most `maxLength` elements. ## Discussion If the maximum length exceeds the number of elements in the collection, the result contains all the elements in the collection. ``` let numbers = [1, 2, 3, 4, 5] print(numbers.prefix(2)) // Prints "[1, 2]" print(numbers.prefix(10)) // Prints "[1, 2, 3, 4, 5]" ``` > Complexity: O(1) if the collection conforms to > `RandomAccessCollection`; otherwise, O(*k*), where *k* is the number of > elements to select from the beginning of the 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)