> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of yjmha69
> Sent: Friday, June 04, 2010 12:28 PM
> To: R-help at r-project.org
> Subject: [R] subsetting a dataframe
>
> Hi there,
> >
a<-data.frame(c(1,2,2,5,9,9),c("A","B","C","D","E","F"))
> > names(a)<-c("x1","x2")
> > max(table(a$x1))
> [1] 2
> >
> The above shows the max count for x1 is 2, which is correct.
> But we can't tell
> there are 2 groups that meet this criteria: 2,2 and 9,9.
> I then want to extract the records that has the hightest count
> > a[max(table(a$x1)),]
> ? x1 x2
> 2? 2? B
> This is not working, since it is equvalent to a[2,]
> What I want is
> ?? x1 x2
> 2 2?? B
> 3 2?? C
> 5 9?? E
> 5 9?? F
>
> I think this should be very easy, but I'm a beginner :-)
One way is to use merge to combine your table with
the original data.frame:
> tmp <- merge(a, as.data.frame(table(a$x1)), by.x="x1",
by.y="Var1")
> tmp[tmp$Freq==max(tmp$Freq), ,drop=FALSE]
Another way is to use ave:
> tmp <- with(a, ave(x1, x1, FUN=length))
> a[tmp==max(tmp), , drop=FALSE]
Another way is
> a[as.character(a$x1) %in% names(tmp[tmp==max(tmp)]), , drop=FALSE]
(This last one might have problems when some values in a$x1
are different but so close that as.character() makes the same
string out of them.)
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
>
> Thanks
>
> YJM
>
>
>
>
>
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