Thank you Tom I really appreciate your help. I want to accept this, but I still don't understand how it works. What does in=in2 do? What is the argument in2? What is the coalesce command doing? ... View more

I see, thanks Tom. That is indeed very useful and needed.   How would I pull over the datetime from file1, as well as the weight? ... View more

Apologies, ballardw. You are correct in that I incorrectly wrote down this problem. The problem should have been: for each date-time in file2, find the LAST date-time and weight that precedes it. Saying "find the first that precedes it" is a bit ambiguous.   I also did have the date-time variable formatted as Tom states below (not as a character variable as I originally posted).   Also, thank you for correcting the semicolon on datalines.   How would you tackle this problem? I would be very grateful for your input!  Kind regards, linlin87 ... View more

Thank you Tom, that is brilliant. It certainly looks to be doing what I was hoping. But why have you introduced this id variable? Because that is not how my data is structured. I do not have this ID variable in my dataset, and I am not sure how this variable you have generated relates to the original data structures. ... View more