Identify and replace duplicates elements from a vector

Question

I have got a vector which is as under

a<- c(1,1,1,2,3,2,2,2,2,1,0,0,0,0,2,3,4,4,1,1)

Here we can see that there are lot of duplicate el

Answer 1

replace(a, duplicated(c(0, cumsum(abs(diff(a))))), 0)
# [1] 1 0 0 2 3 2 0 0 0 1 0 0 0 0 2 3 4 0 1 0

Answer 2

You can created a lagged series and compare

> a
 [1] 1 1 1 2 3 2 2 2 2 1 0 0 0 0 2 3 4 4 1 1
> ifelse(a == c(a[1]-1,a[(1:length(a)-1)]) , 0 , a)
 [1] 1 0 0 2 3 2 0 0 0 1 0 0 0 0 2 3 4 0 1 0