# merging(_:uniquingKeysWith:) Creates a dictionary by merging the given dictionary into this dictionary, using a combining closure to determine the value for duplicate keys. ``` func merging(_ other: [Key : Value], uniquingKeysWith combine: (Value, Value) throws(E) -> Value) throws(E) -> [Key : Value] where E : Error ``` ## Parameters `other` A dictionary to merge. `combine` A closure that takes the current and new values for any duplicate keys. The closure returns the desired value for the final dictionary. ## Return Value A new dictionary with the combined keys and values of this dictionary and `other`. ## Discussion Use the `combine` closure to select a value to use in the returned dictionary, or to combine existing and new values. As the key-value pairs in `other` are merged with this dictionary, the `combine` closure is called with the current and new values for any duplicate keys that are encountered. This example shows how to choose the current or new values for any duplicate keys: ``` let dictionary = ["a": 1, "b": 2] let otherDictionary = ["a": 3, "b": 4] let keepingCurrent = dictionary.merging(otherDictionary) { (current, _) in current } // ["b": 2, "a": 1] let replacingCurrent = dictionary.merging(otherDictionary) { (_, new) in new } // ["b": 4, "a": 3] ``` --- 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)