How to sequentially number a vector in R based on changing unique values?

Question

Assume I have the following vector:

dat <- c(1,1,1, 2,2,2, 3,3, 4,4,4,4)   <- (I added spaces to better see grouping)

I would like to assign sequential numbers starting with 1 restarting for each unique value in dat. The desired result would be:

1 2 3   1 2 3   1 2   1 2 3 4    <- (I added spaces to better see grouping)

My attempt:

unlist(
  lapply(unique(dat), function(x) 
     seq(1,length(which(dat==x)==T),1)
  )
)

[1] 1 2 3 1 2 3 1 2 1 2 3 4

Is there a more straightforward way to do this?

If there is only one run per value: [Numbering rows within groups in a data frame](https://stackoverflow.com/questions/12925063/numbering-rows-within-groups-in-a-data-frame), else [R: count consecutive occurrences of values in a single column](https://stackoverflow.com/questions/19998836/r-count-consecutive-occurrences-of-values-in-a-single-column) — Henrik, Jul 11 '19 at 16:22

score 3 · Answer 1 · answered Jul 11 '19 at 16:19

3

Yes:

sequence(rle(dat)$lengths)

answered Jul 11 '19 at 16:19

joran

Wonderful! That moves much quicker on my data set of 180k rows :). Thanks! – theforestecologist Jul 11 '19 at 16:23
Also, I never knew about `rle()` -- what a great function! – theforestecologist Jul 11 '19 at 16:25

1 Answers1