[R] count number of groups

[William Dunlap]

You did:
> >> ID=c(1,1,1,1,2,2,2,2,3,3,3,3)
> >> as.data.frame(ID)
and I infer that you want the number of groups in each column of
the data.frame.  First, make an example of your data.frame
   D <- data.frame(ID, Name=rep(state.name[1:7],len=length(ID)))
(note I use data.frame, not as.data.frame, so it gets the column
names that I want).  Now use sapply() (or the related vapply()):

> sapply(D, function(column)length(unique(column)))
  ID Name 
   3    7

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Charles Determan Jr
> Sent: Friday, May 25, 2012 9:55 AM
> To: Steve Friedman
> Cc: r-help at r-project.org
> Subject: Re: [R] count number of groups
> 
> That works if I want a count of each group but I needed a count of the
> number of groups.  Michael answered that question with length(unique(ID))
> However, this doesn't supply a title, it is just a number.  I need it to
> still have the identifier 'ID'.
> 
> Regards,
> Charles
> 
> On Fri, May 25, 2012 at 11:50 AM, Steve Friedman <skfglades at gmail.com>wrote:
> 
> > ?table
> > On May 25, 2012 11:46 AM, "Charles Determan Jr" <deter088 at umn.edu> wrote:
> >
> >> Hello,
> >>
> >> Simple question that I am stuck on and can't seem to find an answer in the
> >> help files currently.  I have a list which contains repeated ID's.  I
> >> would
> >> like to have R count the number of ID's.  For example:
> >>
> >> ID=c(1,1,1,1,2,2,2,2,3,3,3,3)
> >> as.data.frame(ID)
> >>
> >> Clearly, there are 3 groups.  How would I have R give me the summary:
> >>
> >> ID
> >> 3
> >>
> >> Many thanks,
> >> Charles
> >>
> >>        [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
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> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.