# compactMap(_:) Creates an asynchronous sequence that maps the given closure over the asynchronous sequence’s elements, omitting results that don’t return a value. ``` @preconcurrency func compactMap(_ transform: @escaping @Sendable (Self.Element) async -> ElementOfResult?) -> AsyncCompactMapSequence ``` ## Parameters `transform` A mapping closure. `transform` accepts an element of this sequence as its parameter and returns a transformed value of the same or of a different type. ## Return Value An asynchronous sequence that contains, in order, the non-`nil` elements produced by the `transform` closure. ## Discussion Use the `compactMap(_:)` method to transform every element received from a base asynchronous sequence, while also discarding any `nil` results from the closure. Typically, you use this to transform from one type of element to another. In this example, an asynchronous sequence called `Counter` produces `Int` values from `1` to `5`. The closure provided to the `compactMap(_:)` method takes each `Int` and looks up a corresponding `String` from a `romanNumeralDict` dictionary. Because there is no key for `4`, the closure returns `nil` in this case, which `compactMap(_:)` omits from the transformed asynchronous sequence. ``` let romanNumeralDict: [Int: String] = [1: "I", 2: "II", 3: "III", 5: "V"] let stream = Counter(howHigh: 5) .compactMap { romanNumeralDict[$0] } for await numeral in stream { print(numeral, terminator: " ") } // Prints "I II III V " ``` --- 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)