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...