# Publisher Operators Methods that create downstream publishers or subscribers to act on the elements they receive. ## Topics ### Mapping elements [`func map((Elements.Element) -> T) -> Publishers.Sequence<[T], Failure>`](/documentation/Combine/Publishers/Sequence/map(_:)) [`func scan(T, (T, Publishers.Sequence.Output) -> T) -> Publishers.Sequence<[T], Failure>`](/documentation/Combine/Publishers/Sequence/scan(_:_:)) [`func setFailureType(to: E.Type) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/setFailureType(to:)) [`func replaceNil(with: T) -> Publishers.Sequence<[Publishers.Sequence.Output], Failure>`](/documentation/Combine/Publishers/Sequence/replaceNil(with:)) ### Filtering elements [`func filter((Publishers.Sequence.Output) -> Bool) -> Publishers.Sequence<[Publishers.Sequence.Output], Failure>`](/documentation/Combine/Publishers/Sequence/filter(_:)) [`func compactMap((Publishers.Sequence.Output) -> T?) -> Publishers.Sequence<[T], Failure>`](/documentation/Combine/Publishers/Sequence/compactMap(_:)) [`func removeDuplicates() -> Publishers.Sequence<[Publishers.Sequence.Output], Failure>`](/documentation/Combine/Publishers/Sequence/removeDuplicates()) ### Reducing elements [`func collect() -> Result<[Publishers.Sequence.Output], Failure>.Publisher`](/documentation/Combine/Publishers/Sequence/collect()) [`func ignoreOutput() -> Empty.Output, Failure>`](/documentation/Combine/Publishers/Sequence/ignoreOutput()) [`func reduce(T, (T, Publishers.Sequence.Output) -> T) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/reduce(_:_:)) [`func tryReduce(T, (T, Publishers.Sequence.Output) throws -> T) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/tryReduce(_:_:)) ### Applying mathematical operations on elements [`func count() -> Just`](/documentation/Combine/Publishers/Sequence/count()-5rrw2) [`func count() -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/count()-5hb52) [`func count() -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/count()-b8ct) [`func max() -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/max()) [`func max(by: (Publishers.Sequence.Output, Publishers.Sequence.Output) -> Bool) -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/max(by:)) [`func min() -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/min()) [`func min(by: (Publishers.Sequence.Output, Publishers.Sequence.Output) -> Bool) -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/min(by:)) ### Applying matching criteria to elements [`func contains(Elements.Element) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/contains(_:)) [`func contains(where: (Publishers.Sequence.Output) -> Bool) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/contains(where:)) [`func tryContains(where: (Publishers.Sequence.Output) throws -> Bool) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/tryContains(where:)) [`func allSatisfy((Publishers.Sequence.Output) -> Bool) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/allSatisfy(_:)) [`func tryAllSatisfy((Publishers.Sequence.Output) throws -> Bool) -> Result.Publisher`](/documentation/Combine/Publishers/Sequence/tryAllSatisfy(_:)) ### Applying sequence operations to elements [`func dropFirst(Int) -> Publishers.Sequence, Failure>`](/documentation/Combine/Publishers/Sequence/dropFirst(_:)) [`func drop(while: (Elements.Element) -> Bool) -> Publishers.Sequence, Failure>`](/documentation/Combine/Publishers/Sequence/drop(while:)) [`func append(S) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/append(_:)-45rm8) [`func append(Publishers.Sequence) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/append(_:)-3dj6k) [`func append(Publishers.Sequence.Output...) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/append(_:)-2knh4) [`func prepend(S) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/prepend(_:)-1r564) [`func prepend(Publishers.Sequence) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/prepend(_:)-71f7p) [`func prepend(Publishers.Sequence.Output...) -> Publishers.Sequence`](/documentation/Combine/Publishers/Sequence/prepend(_:)-2ros1) [`func prefix(Int) -> Publishers.Sequence, Failure>`](/documentation/Combine/Publishers/Sequence/prefix(_:)) [`func prefix(while: (Elements.Element) -> Bool) -> Publishers.Sequence<[Elements.Element], Failure>`](/documentation/Combine/Publishers/Sequence/prefix(while:)) ### Selecting specific elements [`func first() -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/first()) [`func first(where: (Publishers.Sequence.Output) -> Bool) -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/first(where:)) [`func last() -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/last()) [`func last(where: (Publishers.Sequence.Output) -> Bool) -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/last(where:)) [`func output(at: Elements.Index) -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/output(at:)-3r7zo) [`func output(at: Elements.Index) -> Optional.Output>.Publisher`](/documentation/Combine/Publishers/Sequence/output(at:)-9kto7) [`func output(in: Range) -> Publishers.Sequence<[Publishers.Sequence.Output], Failure>`](/documentation/Combine/Publishers/Sequence/output(in:)-6g2zc) [`func output(in: Range) -> Publishers.Sequence<[Publishers.Sequence.Output], Failure>`](/documentation/Combine/Publishers/Sequence/output(in:)-8l6yw) --- 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)