# flatMap(_:) Returns the concatenated results of mapping the given transformation over this sequence. ``` func flatMap(_ transform: @escaping (Self.Elements.Element) -> SegmentOfResult) -> LazySequence>> where SegmentOfResult : Sequence ``` ## Discussion Use this method to receive a single-level sequence when your transformation produces a sequence or collection for each element. Calling `flatMap(_:)` on a sequence `s` is equivalent to calling `s.map(transform).joined()`. > Complexity: O(1) --- 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)