On Thu, Jan 19, 2012 at 6:09 PM, Farrel Buchinsky <[email protected]> wrote: > Oy gevalt!.Am I correct to believe that the technique is rearranging the > data.table so that J can accept the input as pertaining to a secondary key? > That seems as if it is too much work for me and my computer. I will rather > stick to the vector scan methods for now.
Not the entire data.table, just the key columns. Depending on how many queries you're going to make against the 2nd key only, the pay off for your troubles could be anywhere from zero to mucho. Of course if you simply don't have the RAM to make the idx data.table in the first place, then that's that. That's how all indexes work though, no? In a database for instance, if you have a compound key/index over two or more columns, the index will only help queries that work any prefix (or whole) part of the key, and not just any subset elements of it (as you want to do here), right? HTH, -steve -- Steve Lianoglou Graduate Student: Computational Systems Biology | Memorial Sloan-Kettering Cancer Center | Weill Medical College of Cornell University Contact Info: http://cbio.mskcc.org/~lianos/contact _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
