# reduce(into:_:) Returns the result of combining the elements of the asynchronous sequence using the given closure, given a mutable initial value. ``` func reduce(into initialResult: Result, _ updateAccumulatingResult: (inout Result, Self.Element) async throws -> Void) async rethrows -> Result ``` ## Parameters `initialResult` The value to use as the initial accumulating value. The `nextPartialResult` closure receives `initialResult` the first time the closure executes. `updateAccumulatingResult` A closure that combines an accumulating value and an element of the asynchronous sequence into a new accumulating value, for use in the next call of the `nextPartialResult` closure or returned to the caller. ## Return Value The final accumulated value. If the sequence has no elements, the result is `initialResult`. ## Discussion Use the `reduce(into:_:)` method to produce a single value from the elements of an entire sequence. For example, you can use this method on a sequence of numbers to find their sum or product. The `updateAccumulatingResult` closure executes sequentially with an accumulating value initialized to `initialResult` and each element of the sequence. Prefer this method over `reduce(_:_:)` for efficiency when the result is a copy-on-write type, for example an `Array` or `Dictionary`. --- 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)