Create group names for consecutive values

Using rleid from data.table,

library(data.table)

paste0('Group_', rleid(x))
 #[1] "Group_1" "Group_1" "Group_1" "Group_2" "Group_2" "Group_2" "Group_3" "Group_4" "Group_4" "Group_5" "Group_5"

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.)

Using cumsum but not relying on the data being numeric:

paste0("Group_", 1 + c(0, cumsum(x[-length(x)] != x[-1])))


[1] "Group_1" "Group_1" "Group_1" "Group_2" "Group_2" "Group_2" "Group_3" "Group_4" "Group_4" "Group_5" "Group_5"