input sequential numbers without specific end in a data frame's column in r

I would like to give a sequence of numbers to a new column to a data frame. But this sequence will repeat several times based on a value in another column. (i.e It starts from 1 until that specific value will be changed to other value).

My problem is how to define the ending point for each sequence in r.

A part of my data frame with the column "V2" which I intend to add:

  V1      V2(new added column with sequential numbers)           
  12      1
  12      2
  12      3
  12      4
  12      5
  13      1
  13      2
  13      3
  13      4
  13      5
  13      6
  14      1
  14      2
  14      3
  14      4

I tried to use the following code, which was not working!

count <- table(df$V1)
c <- as.integer(names(count)[df$V1==12])
    repeat{
      df$V2<- seq(1,c, by=1)
      if(df$V1!=12){
        break
      }
    }

It sounds like you might be looking for rle since you're interested in any time the "V1" variable changes.

Try the following:

> sequence(rle(df$V1)$lengths)
 [1] 1 2 3 4 5 1 2 3 4 5 6 1 2 3 4