Replace a whole column?

I have a sorted list of data in column B, I have assigned a code to each individual data in column A. Then I have the list of data unsorted in column D. Is it possible, through pivot tables or something, to replace the unsorted data in column D with the codes assigned in A? All at once? Currently I am using the Replace function, and I can only do it one at a time. I have 550 different codes. It will take forever.....