[datatable-help] key disappears after merge of data tables
Matthew Dowle
mdowle at mdowle.plus.com
Tue Jan 18 00:15:20 CET 2011
Just to update this thread, Tom added this FR(#1244). The result of
merge is now keyed when all=FALSE, too. In 1.5.2.
Matthew
On Thu, 2011-01-06 at 10:40 +0000, Matthew Dowle wrote:
> If all is TRUE (or just all.x or all.y is TRUE) then result is keyed.
>
> Why the key is not set when all is FALSE (default) I'm not sure. Tom - can
> you remember? Something to do with NAs in keys seems to ring a bell.
>
> Matthew
>
>
> "Joseph Voelkel" <jgvcqa at rit.edu> wrote in message
> news:70EFCDD908F9264785FA08EC3A47132016CC45F47C at ex02mail01.ad.rit.edu...
> > See code below. When two data tables are merged (by their key
> > variable(s)), that key disappears in the resulting table. While this is
> > probably not strictly a bug, it would seem that the user would most likely
> > want to preserve the key in the output (especially if just enlarging the
> > original data table, e.g. dt2<-merge(dt1,dt2).)
> >
> >
> >> dt1<-data.table(a=1:6,b=11:16,key="a")
> >> dt2<-data.table(a=1:6,c=21:26,key="a")
> >> dt3<-merge(dt1,dt2)
> >>
> >>
> > NAME NROW MB COLS KEY
> > [1,] dt1 6 1 a,b a
> > [2,] dt2 6 1 a,c a
> > [3,] dt3 6 1 a,b,c
> > Total: 3MB
> >
> >
> > Joseph G. Voelkel, Ph.D.
> > Professor, Center for Quality and Applied Statistics
> > Kate Gleason College of Engineering
> > Rochester Institute of Technology
> > V 585-475-2231
> > F 585-475-5959
> > joseph.voelkel at rit.edu
>
>
>
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