Functional Methods
Note
Open
Functional.playground at the
Methods page.
Note
The following sections show different ways of performing the same tasks. They say nothing about which version is better.
filter
The
filter method
looks like this:
func filter(_ isIncluded: (Element) throws -> Bool) rethrows -> [Element]
It is
a simple method on
Sequence, and we have already used it. The input function takes an element of the sequence and returns either
false or
true.
filter returns an array of only those elements for which the input function returns
true:
let numbers = [-4,4,2,-8,0]
let negative = numbers.filter {$0<0} // [-4, -8]
Set and
Dictionary have their own versions of this method, which return a Set or Dictionary respectively.
Using the filter Method
It is often simpler to use an existing collection that has everything we want, and filter it, than creating an empty collection...
