Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection.
SDK
- Xcode 9.0+
Framework
- Swift Standard Library
Declaration
func prefix(_ maxLength: Int) -> Slice<Dictionary<Key, Value>.Keys>
Parameters
maxLengthThe maximum number of elements to return.
maxmust be greater than or equal to zero.Length
Return Value
A subsequence starting at the beginning of this collection with at most max elements.
Discussion
If the maximum length exceeds the number of elements in the collection, the result contains all the elements in the collection.
let numbers = [1, 2, 3, 4, 5]
print(numbers.prefix(2))
// Prints "[1, 2]"
print(numbers.prefix(10))
// Prints "[1, 2, 3, 4, 5]"
Complexity: O(1) if the collection conforms to Random; otherwise, O(k), where k is the number of elements to select from the beginning of the collection.