# reduce(_:_:) Returns the result of combining the elements of the asynchronous sequence using the given closure. ``` func reduce(_ initialResult: Result, _ nextPartialResult: (Result, Self.Element) async throws -> Result) async rethrows -> Result ``` ## Parameters `initialResult` The value to use as the initial accumulating value. The `nextPartialResult` closure receives `initialResult` the first time the closure runs. `nextPartialResult` 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(_:_:)` method to produce a single value from the elements of an entire sequence. For example, you can use this method on an sequence of numbers to find their sum or product. The `nextPartialResult` closure executes sequentially with an accumulating value initialized to `initialResult` and each element of the sequence. In this example, an asynchronous sequence called `Counter` produces `Int` values from `1` to `4`. The `reduce(_:_:)` method sums the values received from the asynchronous sequence. ``` let sum = await Counter(howHigh: 4) .reduce(0) { $0 + $1 } print(sum) // Prints "10" ``` --- 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)