[R] tapply

[Liaw, Andy]

What does str(z) say?  I suspect the second column is a factor, which, after
the subsetting, has some empty levels.  If so, just drop those levels.

Andy

> From: Weiwei Shi
> 
> hi
> i tried all the methods suggested above:
> ave and rowsum with "with" function works for my situation. I think
> the problem might not be due to tapply.
> My data z comes from
> z<-y[y[[1]] %in% x[[2]], c(1,9)]
> 
> while z is supposed to have no entries for those non-matched 
> between x and y.
> 
> however, when I run tapply, and the result also includes those
> non-matched entries. I use is.na function to remove those entry from z
> first and then use tapply again, but the result is the same: those
> NA's and those non-matched results are still there. That's what I mean
> by "it doesn't work".
> 
> Is there something I missed here so that z "implicitly" has some
> "trace" back to y dataset?
> 
> thanks,
> 
> On 6/20/05, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> > On 6/20/05, Weiwei Shi <helprhelp at gmail.com> wrote:
> > > hi,
> > > i have another question on tapply:
> > > i have a dataset z like this:
> > > 5540 389100307391      2600
> > > 5541 389100307391      2600
> > > 5542 389100307391      2600
> > > 5543 389100307391      2600
> > > 5544 389100307391      2600
> > > 5546 381300302513        NA
> > > 5547 387000307470        NA
> > > 5548 387000307470        NA
> > > 5549 387000307470        NA
> > > 5550 387000307470        NA
> > > 5551 387000307470        NA
> > > 5552 387000307470        NA
> > >
> > > I want to sum the column 3 by column 2.
> > > I removed NA by calling:
> > > tapply(z[[3]], z[[2]], sum, na.rm=T)
> > > but it does not work.
> > >
> > > then, i used
> > > z1<-z[!is.na(z[[3]],]
> > > and repeat
> > > still doesn't work.
> > >
> > > please help.
> > >
> > 
> > Depending on what you want you may be able to use rowsum:
> > 
> > - display only groups that have at least one non-NA with the sum
> >   being the sum of the non-NAs:
> > 
> >         with(na.omit(z), rowsum(V3, V2))
> > 
> > - display all groups with the sum being NA if any member is NA:
> > 
> >         rowsum(z$V3, z$V2)
> > 
> 
> 
> -- 
> Weiwei Shi, Ph.D
> 
> "Did you always know?"
> "No, I did not. But I believed..."
> ---Matrix III
> 
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