---
title: "removeDuplicates(by:)"
framework: combine
role: symbol
role_heading: Instance Method
path: "combine/publisher/removeduplicates(by:)"
---

# removeDuplicates(by:)

Publishes only elements that don’t match the previous element, as evaluated by a provided closure.

## Declaration

```swift
func removeDuplicates(by predicate: @escaping (Self.Output, Self.Output) -> Bool) -> Publishers.RemoveDuplicates<Self>
```

## Parameters

- `predicate`: A closure to evaluate whether two elements are equivalent, for purposes of filtering. Return true from this closure to indicate that the second element is a duplicate of the first.

## Return Value

Return Value A publisher that consumes — rather than publishes — duplicate elements.

## Discussion

Discussion Use removeDuplicates(by:) to remove repeating elements from an upstream publisher based upon the evaluation of the current and previously published elements using a closure you provide. Use the removeDuplicates(by:) operator when comparing types that don’t themselves implement Equatable, or if you need to compare values differently than the type’s Equatable implementation. In the example below, the removeDuplicates(by:) functionality triggers when the x property of the current and previous elements are equal, otherwise the operator publishes the current Point to the downstream subscriber: struct Point {     let x: Int     let y: Int }

let points = [Point(x: 0, y: 0), Point(x: 0, y: 1),               Point(x: 1, y: 1), Point(x: 2, y: 1)] cancellable = points.publisher     .removeDuplicates { prev, current in         // Considers points to be duplicate if the x coordinate         // is equal, and ignores the y coordinate         prev.x == current.x     }     .sink { print("\($0)", terminator: " ") }

// Prints: Point(x: 0, y: 0) Point(x: 1, y: 1) Point(x: 2, y: 1)

## See Also

### Filtering elements

- [filter(_:)](combine/publisher/filter(_:).md)
- [tryFilter(_:)](combine/publisher/tryfilter(_:).md)
- [compactMap(_:)](combine/publisher/compactmap(_:).md)
- [tryCompactMap(_:)](combine/publisher/trycompactmap(_:).md)
- [removeDuplicates()](combine/publisher/removeduplicates().md)
- [tryRemoveDuplicates(by:)](combine/publisher/tryremoveduplicates(by:).md)
- [replaceEmpty(with:)](combine/publisher/replaceempty(with:).md)
- [replaceError(with:)](combine/publisher/replaceerror(with:).md)