Is there a dplyr equivalent to data.table::rleid?
You can just do (when you have both data.table and dplyr loaded):
DT <- DT %>% mutate(rlid = rleid(grp))
this gives:
> DT grp value rlid 1: A 1 1 2: A 2 1 3: B 3 2 4: B 4 2 5: C 5 3 6: C 6 3 7: C 7 3 8: A 8 4 9: B 9 5 10: B 10 5
When you don't want to load data.table separately you can also use (as mentioned by @DavidArenburg in the comments):
DT <- DT %>% mutate(rlid = data.table::rleid(grp))
And as @RichardScriven said in his comment you can just copy/steal it:
myrleid <- data.table::rleid
If you want to use just base R and dplyr, the better way is to wrap up your own one or two line version of rleid()
as a function and then apply that whenever you need it.
library(dplyr)
myrleid <- function(x) {
x <- rle(x)$lengths
rep(seq_along(x), times=x)
}
## Try it out
DT <- DT %>% mutate(rlid = myrleid(grp))
DT
# grp value rlid
# 1: A 1 1
# 2: A 2 1
# 3: B 3 2
# 4: B 4 2
# 5: C 5 3
# 6: C 6 3
# 7: C 7 3
# 8: A 8 4
# 9: B 9 5
#10: B 10 5
You can do it using the lag
function from dplyr
.
DT <-
DT %>%
mutate(rleid = (grp != lag(grp, 1, default = "asdf"))) %>%
mutate(rleid = cumsum(rleid))
gives
> DT
grp value rleid
1: A 1 1
2: A 2 1
3: B 3 2
4: B 4 2
5: C 5 3
6: C 6 3
7: C 7 3
8: A 8 4
9: B 9 5
10: B 10 5