R cumunique like cumsum [duplicate]

Answer 1

We can try

library(zoo)
a[duplicated(a)] <- NA
a[!is.na(a)] <- seq_along(a[!is.na(a)])
na.locf(a)
#[1] 1 2 3 4 4 5 5 5

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Or another option is

cumsum(ave(a, a, FUN=seq_along)==1)
#[1] 1 2 3 4 4 5 5 5

Or a compact option would be

library(splitstackshape)
getanID(a)[, cumsum(.id==1)]
#[1] 1 2 3 4 4 5 5 5

Answer 2

You can try:

cumsum(!duplicated(a))
#[1] 1 2 3 4 4 5 5 5