Array extension for grouping its values

ArrayExtensions.swift

extension Array {
    func grouped<T: Equatable>(by value: (Element) -> T) -> [[Element]] {
        var result = [[Element]]()
        for element in self {
            var foundIndex: Int?
            for (index, internalArray) in result.enumerated() {
                if let firstValue = internalArray.first, value(firstValue) == value(element) {
                    foundIndex = index
                    continue
                }
            }
            foundIndex == nil ? result.append([element]) : result[foundIndex!].append(element)
        }
        return result
    }
}

Examples

let ints = [1,2,3,1,2,3,3,3]
let intsGrouped = ints.grouped(by: { $0 })
print(intsGrouped)

let dates = [Date(), Date().addingTimeInterval(-86400), Date().addingTimeInterval(-86400)]
let datesGrouped = dates.grouped(by: {$0.day})
print(datesGrouped)

intsGrouped:
[[1, 1], [2, 2], [3, 3, 3, 3]]

datesGrouped:
[[2018-12-12 16:20:05], [2018-12-11 16:20:05, 2018-12-11 16:20:05]]