Returns a new dictionary containing only the key-value pairs that have non-nil values as the result of transformation by the given closure.
SDK
- Xcode 10.2+
Framework
- Swift Standard Library
Declaration
func compactMapValues<T>(_ transform: (Value) throws -> T?) rethrows -> Dictionary<Key, T>
Parameters
transformA closure that transforms a value.
transformaccepts each value of the dictionary as its parameter and returns an optional transformed value of the same or of a different type.
Return Value
A dictionary containing the keys and non-nil transformed values of this dictionary.
Discussion
Use this method to receive a dictionary with non-optional values when your transformation produces optional values.
In this example, note the difference in the result of using map and compact with a transformation that returns an optional Int value.
let data = ["a": "1", "b": "three", "c": "///4///"]
let m: [String: Int?] = data.mapValues { str in Int(str) }
// ["a": 1, "b": nil, "c": nil]
let c: [String: Int] = data.compactMapValues { str in Int(str) }
// ["a": 1]
Complexity: O(m + n), where n is the length of the original dictionary and m is the length of the resulting dictionary.