subtraction doesn't work for multiple values in one field

I managed to create a table that somewhat looks like this: ![alt text][1] However, when I tried to append a new column with the differences between after and before as its value, it just gave me a blank space. I used `eval differences=after-before` which apparently doesn't work. Is there some other workaround on this? I need to get the list of differences so the end result should look something like below: ![alt text][2] I need to have that column so I can process the average, min, and max difference for each name1, name2, etc. Thanks! [1]: /storage/temp/75247-splunk-table.png [2]: /storage/temp/75248-splunk-table2.png