Thanks Matthew I was just trying something and saw this.
I can get what I want using unique with a data.frame. It gives the result one would expect. This did make me somewhat scared that using a "by" statement with a data.table on multiple key might skip some unique combinations. Damian Damian Betebenner Center for Assessment PO Box 351 Dover, NH 03821-0351 Phone (office): (603) 516-7900 Phone (cell): (857) 234-2474 Fax: (603) 516-7910 [email protected] www.nciea.org -----Original Message----- From: Matthew Dowle [mailto:[email protected]] On Behalf Of Matthew Dowle Sent: Saturday, June 25, 2011 8:27 PM To: Damian Betebenner Cc: [email protected] Subject: Re: [datatable-help] unique The NA in the key seems to be the issue. duplicated.data.table calls diff on the columns and assumes no NA in keys. Can't remember - did we decide to disallow NA in keys? There were other issues with NA in keys and some threads in the past. Do you need the key to contain NA? Matthew On Sat, 2011-06-25 at 16:23 -0500, Damian Betebenner wrote: > All, > > > > I have a simple question regarding the behavior of unique with more > than 1 key. Consider the example: > > > > > dt <- data.table(X=c(NA,1,2,3), Y=c(NA,2,1,3)) > > > dt > > X Y > > [1,] NA NA > > [2,] 1 2 > > [3,] 2 1 > > [4,] 3 3 > > > key(dt) <- c("X", "Y") > > > unique(dt) > > X Y > > [1,] NA NA > > [2,] 2 1 > > [3,] 3 3 > > > > If I understand this correctly, unique see rows 2 and 3 of dt as the > same. > > > > Is this the behavior one wants? > > > > Thanks for any clarification. > > > > Damian > > > > > > > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
