Concatenate values based on criteria

Question

I have a two column list of data in Excel. The first column being a question number from a test and the second column being a number referencing what is being tested on that

Answer 1

Just to put my comment in an answer, so it make more sense.

First sort columns A and B on Column B.

In C2 put the formula:

=IF(B2=B3,A2&","&C3,A2)

Then copy down.

Then in Column E place your unique reference list. And in D2 put:

=VLOOKUP(E2,$B$2:$C$6,2,FALSE)

And copy down.

You can then hide column C.

It does require that it be sorted correctly and a helper column but it does stay to the formulas only rule.