Sorry for the confusion. Let me explain:   The one you posted is not a match for me because I would like "nearest" match. By "nearest", I mean within +/- two quarters for a given firm, so 2000Q1 shouldn't be related to 2001Q3 - but your idea is exactly right, the following should also be a valid match (which is missing from the original post)          AA        2001        4        -50        0        2002Q1          AA        2001        4        -50        50        2002Q2    Another clarification is about the case of firm BB - they don't have common entry as the other matches. The reason I post it here is that I have no idea how I should deal with such case, and any ideas would be extremely appreciated. The original data is about cash flows - a story would be that I earn 50 in 2000Q4 and 100 in 2001Q1, and I spent 100 each in 2001Q3 and 2001Q4. I manually checked and the data is consistent with my story. ... View more