Search code examples
rcountsequencefind-occurrencesrun-length-encoding

Create counter within consecutive runs of values

I wish to create a sequential number within each run of equal values, like a counter of occurrences, which restarts once the value in the current row is different from the previous row.

Please find an example of input and expected output below.

dataset <- data.frame(input = c("a","b","b","a","a","c","a","a","a","a","b","c"))
dataset$counter <- c(1,1,2,1,2,1,1,2,3,4,1,1)
dataset

#    input counter
# 1      a       1
# 2      b       1
# 3      b       2
# 4      a       1
# 5      a       2
# 6      c       1
# 7      a       1
# 8      a       2
# 9      a       3
# 10     a       4
# 11     b       1
# 12     c       1

My question is very similar to this one: Cumulative sequence of occurrences of values.

Solution

  • You need to use sequence and rle:

    > sequence(rle(as.character(dataset$input))$lengths)
 [1] 1 1 2 1 2 1 1 2 3 4 1 1