let calculateSeries = function
    | [] -> []
    | x :: xs ->
        let length, _, lastSeriesLength, otherSeries =
            List.fold (fun (i, thisSeriesValue, thisSeriesLength, otherSeries) x ->
                if x = thisSeriesValue then
                    i+1, thisSeriesValue, thisSeriesLength+1, otherSeries
                else
                    i+1, x, 1, (i - thisSeriesLength + 1, thisSeriesLength) :: otherSeries
            ) (0, x, 1, []) xs
        (length - lastSeriesLength + 1, lastSeriesLength) :: otherSeries
        |> List.rev