Adjacent identical elements in vector in R

Question

Is there an efficient way in R to recognize adjacent identical elements ?

Let's say I have this vector:

(Vx)
1 2 2 1 3 3 3 1 2 2 3 3 0

And I'd like to get:

0 1 1 0 1 1 1 0 1 1 1 1 0 

Is there any clean way to do this ? I'm trying to avoid loops or cumbersome functions but so far I haven't had any luck.

Thanks.

Answer 1

vec <- c(1, 2, 2, 1, 3, 3, 3, 1, 2, 2, 3, 3, 0)

l <-  rle(vec)$lengths

rep(ifelse(l == 1, 0, 1), times = l)

# [1] 0 1 1 0 1 1 1 0 1 1 1 1 0

Answer 2

Try rle and inverse.rle like this:

r <- rle(vx)
r$values <- (r$lengths > 1) + 0
inverse.rle(r)

giving:

[1] 0 1 1 0 1 1 1 0 1 1 1 1 0