It sounds like you have an array J and you want to map each element of J to a unique integer in 1:N for N as small as possible? This will do it:
d = (Int=>eltype(J))[j => i for (i,j) in enumerate(unique(J))] Jcodes = [d[j] for j in J] Here, d is a dictionary mapping integers in 1:N to the corresponding values in J, and Jcodes is the "re-coded" array.
