Thanks Jim! I posted the specifics of what I'm trying to accomplish here: http://r.789695.n4.nabble.com/Slow-Data-Table-Merge-td3072027.html -- View this message in context: http://r.789695.n4.nabble.com/Non-visible-functions-merge-data-table-tp3072051p3072075.html Sent from the R help mailing list archive at Nabble.com.