map_swift

func frequency(numbers: [Int]) -> [Int: Int] {
    var frequencyDictionary: [Int:Int] = [:]
    for number in numbers {
        if let existentValue = frequencyDictionary[number] {
            frequencyDictionary[number] = existentValue + 1
        } else {
            frequencyDictionary[number] = 1
        }
    }
    return frequencyDictionary
}

print(frequency(numbers: [1, 3, 1, 1, 2, 7, 3, 5, 8, 5, 4, 9]))