Returns the result of combining the elements of the sequence using the given closure.
- Xcode 9.0+
- Swift Standard Library
The value to use as the initial accumulating value.
A closure that updates the accumulating value with an element of the sequence.
The final accumulated value. If the sequence has no elements, the result is
reduce(into: method to produce a single value from the elements of an entire sequence. For example, you can use this method on an array of integers to filter adjacent equal entries or count frequencies.
This method is preferred over
reduce(_: for efficiency when the result is a copy-on-write type, for example an Array or a Dictionary.
update closure is called sequentially with a mutable accumulating value initialized to
initial and each element of the sequence. This example shows how to build a dictionary of letter frequencies of a string.
letters is called, the following steps occur:
updateclosure is called with the initial accumulating value—
[:]in this case—and the first character of
letters, modifying the accumulating value by setting
1for the key
The closure is called again repeatedly with the updated accumulating value and each element of the sequence.
When the sequence is exhausted, the accumulating value is returned to the caller.
If the sequence has no elements,
update is never executed and
initial is the result of the call to
Complexity: O(n), where n is the length of the sequence.