Chunk an array into subarrays

chunk.swift

extension Array {
    func chunk<T : Equatable>(by valueToCompare: (Element) -> T) -> [[Element]] {
        var currentValue = self[0]
        var startIndex = 0
        var splits = [[Element]]()
        for (index, value) in self.enumerate() {
            if valueToCompare(value) != valueToCompare(currentValue) {
                let newSplit = self[startIndex..<index]
                splits.append(Array(newSplit))
                startIndex = index
                currentValue = value
            }
        }
        let newSplit = self[startIndex..<self.count]
        splits.append(Array(newSplit))
        return splits
    }
}