sorry to bother you. I have a data.frame like this: 24.8 23.2 22.8 22.5 22.5 22.4 22.4 22.4 22.3 22.2 22.2 22.2 22 21.9 21.9 21.8 I would like to add an index according to the frequency, to have the following output: 24.8 1 23.2 1 22.8 1 22.5 2 22.5 2 22.4 3 22.4 3 22.4 3 22.3 1 22.2 3 22.2 3 22.2 3 22 1 21.9 2 21.9 2 21.8 1 How this can be done? in other words, since 28.8 occurs 1 time, it will have the index 1; since 22.5 occurs two times, it will have index 2 and so on.