R Regular Expression Lookbehind

Question

I have a vector filled with strings of the following format:

the first entries of the vector looks like

Answer 1

Since this is fixed format, why not use substr? year1 is extracted using substr(s,1,4), id1 is extracted using substr(s,9,9) and the id2 as as.numeric(substr(s,10,13)). In the last case I used as.numeric to get rid of the zeroes.