Applying cumsum to binary vector

Question

I have a simple binary vector a which I try to translate into vector b using the R function cumsum. However, cumsum does not

Answer 1

The trick is to use diff to mark the transitions:

cumsum(as.logical(a+c(0,abs(diff(a)))))
 [1]  1  2  2  2  3  4  5  6  7  7  8  9  9  9 10 11