Non-Equi Joins in data.table

John MacKintosh wants to join on a greater than or less than operation:

For day 5, I had to create a function, and I’m writing this up, because it’s an example of a non-equi join between two tables.
In this particular sitation, there are are no common columns between the two tables, so my usual data.table hack of copying the columns of interest, renaming themjoin_col, and then keying them both does not work.

Click through for a working solution.