rrun-length-encoding

Create group names for consecutive values

Looks like an easy task, can't figure out a simpler way. I have an x vector below, and need to create group names for consecutive values. My attempt was using rle, better ideas?

# data
x <- c(1,1,1,2,2,2,3,2,2,1,1)

# make groups
rep(paste0("Group_", 1:length(rle(x)$lengths)), rle(x)$lengths)
# [1] "Group_1" "Group_1" "Group_1" "Group_2" "Group_2" "Group_2" "Group_3" "Group_4"
# [9] "Group_4" "Group_5" "Group_5"
Solution

  • Using diff and cumsum :

    paste0("Group_", cumsum(c(1, diff(x) != 0)))
#[1] "Group_1" "Group_1" "Group_1" "Group_2" "Group_2" "Group_2" "Group_3" "Group_4" "Group_4" "Group_5" "Group_5"

    (If your values are floating point values, you might have to avoid != and use a tolerance instead.)