How to count matching items in an array
Swift version: 5.2
If you want to count how many items in an array (or any collection) match a test you specify, the easiest thing to do is run the collection through a call to filter() then count the remainder.
For example, if you had an array of numbers and wanted to count how many were odd, you would write this:
let count1 = [1, 2, 3, 4, 5].filter { $0 % 2 == 1 }.countBecause this is something that all collections might want to do, you should consider wrapping it in an extension on Collection, like this:
extension Collection {
func count(where test: (Element) throws -> Bool) rethrows -> Int {
return try self.filter(test).count
}
}With that change, counting the odd numbers becomes this:
let count2 = [1, 2, 3, 4, 5].count { $0 % 2 == 1 }
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Available from iOS 8.0
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