# indices(where:) Returns the indices of all the elements that match the given predicate. ``` func indices(where predicate: (Self.Element) throws -> Bool) rethrows -> RangeSet ``` ## Parameters `predicate` A closure that takes an element as its argument and returns a Boolean value that indicates whether the passed element represents a match. ## Return Value A set of the indices of the elements for which `predicate` returns `true`. ## Discussion For example, you can use this method to find all the places that a vowel occurs in a string. ``` let str = "Fresh cheese in a breeze" let vowels: Set = ["a", "e", "i", "o", "u"] let allTheVowels = str.indices(where: { vowels.contains($0) }) // str[allTheVowels].count == 9 ``` > Complexity: O(*n*), where *n* is the length 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)