count(where:)

Declaration

func count<E>(where predicate: (Self.Element) throws(E) -> Bool) throws(E) -> Int where E : Error

Parameters

• predicate:

  A closure that takes each element of the sequence as its argument and returns a Boolean value indicating whether the element should be included in the count.

Return Value

The number of elements in the sequence that satisfy the given predicate.

Discussion

You can use this method to count the number of elements that pass a test. The following example finds the number of names that are fewer than five characters long:

let names = ["Jacqueline", "Ian", "Amy", "Juan", "Soroush", "Tiffany"]
let shortNameCount = names.count(where: { $0.count < 5 })
// shortNameCount == 3

To find the number of times a specific element appears in the sequence, use the equal to operator (==) in the closure to test for a match.

let birds = ["duck", "duck", "duck", "duck", "goose"]
let duckCount = birds.count(where: { $0 == "duck" })
// duckCount == 4

The sequence must be finite.