Efficient way in Swift to trim an array

Question

Let's say I have a struct…

struct Person {
   let isMale: Bool
   let name: String
}

and an array of Person structs. I want to trim all the men (isMale == true) from the start and end of the array (similarly to how you'd trim whitespace from the start & end of a string)…

func trimMen(people: [Person]) -> [Person]

    var trimmedPeople: [Person] = people

    while trimmedPeople.first?.isMale {
        trimmedPeople.removeFirst()
    }
    while trimmedPeople.last?.isMale {
        trimmedPeople.removeLast()
    }
    return trimmedPeople
}

Is there a more efficient way to do it?

Answer 1

Following implementation provides generic solution, which mimics other foundation methods like filter, map etc. Though extends Array instead of SequenceType.

Main benefit from this solution comparing to the original provided by Ashley Mills is that it does not mutate an array.

extension Array {

    func trim(@noescape predicate: (Element) throws -> Bool) rethrows -> [Element] {
        guard let
            start = try (indexOf { try !predicate($0) }),
            end = try (reverse().indexOf { try !predicate($0) }) else {
                return []
        }
        return Array(self[start..<end.base])
    }

}

Usage Example:

persons.trim { $0.isMale }

Answer 2

Swift 3.1 has solved this problem with drop(while:) and prefix(while:)

struct Person {
    let isMale: Bool
    let name: String
}

let people = [Person(isMale: true, name: "Bill"),
              Person(isMale: false, name: "Jane"),
              Person(isMale: true, name: "José"),
              Person(isMale: false, name: "Sarah"),
              Person(isMale: true, name: "Steve"),
              Person(isMale: true, name: "Tony")]

func trimMen(people: [Person]) -> [Person] {
    let removedPrefixMen = people.drop { $0.isMale }
    let removedSuffixMen = removedPrefixMen.reversed().drop { $0.isMale }
    return removedSuffixMen.reversed()
}

// [{isMale false, name "Jane"}, {isMale true, name "José"}, {isMale false, name "Sarah"}]

Also in Swift 3.1, concrete constrained extensions, means I can do this…

extension Array where Element == Person {

    func trimMen() -> [Element] {
        let removedPrefixMen = drop{ $0.isMale }
        let removedSuffixMen = removedPrefixMen.reversed().drop{ $0.isMale }
        return removedSuffixMen.reversed()
    }
}

people.trimMen()