# Publisher Operators Methods that create downstream publishers or subscribers to act on the elements they receive. ## Topics ### Mapping elements [`func map((Output) -> T) -> Just`](/documentation/Combine/Just/map(_:)) [`func tryMap((Output) throws -> T) -> Result.Publisher`](/documentation/Combine/Just/tryMap(_:)) [`func mapError((Just

.Failure) -> E) -> Result.Publisher`](/documentation/Combine/Just/mapError(_:)) [`func scan(T, (T, Output) -> T) -> Result.Failure>.Publisher`](/documentation/Combine/Just/scan(_:_:)) [`func tryScan(T, (T, Output) throws -> T) -> Result.Publisher`](/documentation/Combine/Just/tryScan(_:_:)) [`func setFailureType(to: E.Type) -> Result.Publisher`](/documentation/Combine/Just/setFailureType(to:)) ### Filtering elements [`func filter((Output) -> Bool) -> Optional

.Publisher`](/documentation/Combine/Just/filter(_:)) [`func compactMap((Output) -> T?) -> Optional.Publisher`](/documentation/Combine/Just/compactMap(_:)) [`func removeDuplicates() -> Just

`](/documentation/Combine/Just/removeDuplicates()) [`func removeDuplicates(by: (Output, Output) -> Bool) -> Just

`](/documentation/Combine/Just/removeDuplicates(by:)) [`func tryRemoveDuplicates(by: (Output, Output) throws -> Bool) -> Result.Publisher`](/documentation/Combine/Just/tryRemoveDuplicates(by:)) [`func replaceEmpty(with: Output) -> Just

`](/documentation/Combine/Just/replaceEmpty(with:)) [`func replaceError(with: Output) -> Just

`](/documentation/Combine/Just/replaceError(with:)) ### Reducing elements [`func collect() -> Just<[Output]>`](/documentation/Combine/Just/collect()) [`func ignoreOutput() -> Empty.Failure>`](/documentation/Combine/Just/ignoreOutput()) [`func reduce(T, (T, Output) -> T) -> Result.Failure>.Publisher`](/documentation/Combine/Just/reduce(_:_:)) [`func tryReduce(T, (T, Output) throws -> T) -> Result.Publisher`](/documentation/Combine/Just/tryReduce(_:_:)) ### Applying mathematical operations on elements [`func count() -> Just`](/documentation/Combine/Just/count()) [`func max() -> Just

`](/documentation/Combine/Just/max()) [`func max(by: (Output, Output) -> Bool) -> Just

`](/documentation/Combine/Just/max(by:)) [`func min() -> Just

`](/documentation/Combine/Just/min()) [`func min(by: (Output, Output) -> Bool) -> Just

`](/documentation/Combine/Just/min(by:)) ### Applying matching criteria to elements [`func contains(Output) -> Just`](/documentation/Combine/Just/contains(_:)) [`func contains(where: (Output) -> Bool) -> Just`](/documentation/Combine/Just/contains(where:)) [`func tryContains(where: (Output) throws -> Bool) -> Result.Publisher`](/documentation/Combine/Just/tryContains(where:)) [`func allSatisfy((Output) -> Bool) -> Just`](/documentation/Combine/Just/allSatisfy(_:)) [`func tryAllSatisfy((Output) throws -> Bool) -> Result.Publisher`](/documentation/Combine/Just/tryAllSatisfy(_:)) ### Applying sequence operations to elements [`func dropFirst(Int) -> Optional

.Publisher`](/documentation/Combine/Just/dropFirst(_:)) [`func drop(while: (Output) -> Bool) -> Optional

.Publisher`](/documentation/Combine/Just/drop(while:)) [`func append(Output...) -> Publishers.Sequence<[Output], Just

.Failure>`](/documentation/Combine/Just/append(_:)-7eyqj) [`func append(S) -> Publishers.Sequence<[Output], Just

.Failure>`](/documentation/Combine/Just/append(_:)-7sxlu) [`func prepend(S) -> Publishers.Sequence<[Output], Just

.Failure>`](/documentation/Combine/Just/prepend(_:)-39e57) [`func prepend(Output...) -> Publishers.Sequence<[Output], Just

.Failure>`](/documentation/Combine/Just/prepend(_:)-7fg73) [`func prefix(Int) -> Optional

.Publisher`](/documentation/Combine/Just/prefix(_:)) [`func prefix(while: (Output) -> Bool) -> Optional

.Publisher`](/documentation/Combine/Just/prefix(while:)) ### Selecting specific elements [`func first() -> Just

`](/documentation/Combine/Just/first()) [`func first(where: (Output) -> Bool) -> Optional

.Publisher`](/documentation/Combine/Just/first(where:)) [`func last() -> Just

`](/documentation/Combine/Just/last()) [`func last(where: (Output) -> Bool) -> Optional

.Publisher`](/documentation/Combine/Just/last(where:)) [`func output(at: Int) -> Optional

.Publisher`](/documentation/Combine/Just/output(at:)) [`func output(in: R) -> Optional

.Publisher`](/documentation/Combine/Just/output(in:)) ### Handling errors [`func retry(Int) -> Just

`](/documentation/Combine/Just/retry(_:)) --- 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)