Array+mode.swft

import Foundation

extension Array where Element: Hashable {
    /// Returns most popular member of the array
    ///
    /// - SeeAlso: https://en.wikipedia.org/wiki/Mode_(statistics)
    ///
    typealias ArrayMode = (item: Element?, count: Int)

    func mode() -> (item: Element?, count: Int) {

        let countedSet = NSCountedSet(array: self)
        let counts: [ArrayMode] = countedSet.objectEnumerator()
            .map { 
                let item = $0 as? Element
                return ArrayMode(item: item,
                                count: countedSet.count(for: $0))
            }
        let emptyResult = ArrayMode(item: nil,
                                   count: 0)
        return counts.reduce(emptyResult) {
            return ($0.count > $1.count) ? $0 : $1
        }
    }

}

[5,5,1,4,2,5,3,3,4,1,5].mode()  // ({some 5}, .1 4)