Actually it can be done with xtabs if that's the approach you prefer.
 > foo$yr <- factor(foo$yr)
> margin.table(xtabs(~ div + yr, foo), 2)
yr
1998 1999 2000 
0 4 2 
> margin.table(xtabs(~ org + yr, foo), 2)
yr
1998 1999 2000 
4 4 2 


 On 4/26/05, Andy Bunn <abunn@whrc.org> wrote: 
> 
> The three was a typo, which I regret very much. I don't know why I didn't
> think of apply. I was obsessed with doing it as a table.
> Thanks for your response,
> -Andy
> 
> > -----Original Message-----
> > From: Tony Plate [mailto:tplate@acm.org]
> > Sent: Tuesday, April 26, 2005 2:00 PM
> > To: Andy Bunn
> > Cc: R-Help
> > Subject: Re: [R] Summarizing factor data in table?
> >
> >
> > Do you want to count the number of non-NA divisions and organizations in
> > the data for each year (where duplicates are counted as many times as
> > they appear)?
> >
> > > tapply(!is.na(foo$div), foo$yr, sum)
> > 1998 1999 2000
> > 0 4 2
> > > tapply(!is.na(foo$org), foo$yr, sum)
> > 1998 1999 2000
> > 4 4 2
> > >
> >
> > Or perhaps the number of unique non-NA divisions and organizations in
> > the data for each year?
> >
> > > tapply(foo$div, foo$yr, function(x) length(na.omit(unique(x))))
> > 1998 1999 2000
> > 0 4 2
> > > tapply(foo$org, foo$yr, function(x) length(na.omit(unique(x))))
> > 1998 1999 2000
> > 4 4 2
> > >
> >
> > (I don't understand where the "3" in your desired output comes from
> > though, which maybe indicates I completely misunderstand your request.)
> >
> > Andy Bunn wrote:
> > > I have a very simple query with regard to summarizing the
> > number of factors
> > > present in a certain snippet of a data frame.
> > > Given the following data frame:
> > >
> > > foo <- data.frame(yr = c(rep(1998,4), rep(1999,4),
> > rep(2000,2)), div =
> > > factor(c(rep(NA,4),"A","B","C","D","A","C")),
> > > org = factor(c(1:4,1:4,1,2)))
> > >
> > > I want to get two new variables. Object ndiv would give the number of
> > > divisions by year:
> > > 1998 0
> > > 1999 3
> > > 2000 2
> > > Object norgs would give the number of organizations
> > > 1998 4
> > > 1999 4
> > > 2000 2
> > > I figure xtabs should be able to do it, but I'm stuck without a
> > for loop.
> > > Any suggestions? -Andy
> > >
> > > ______________________________________________
> > > R-help@stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide!
> > http://www.R-project.org/posting-guide.html
> > >
> >
> >
> 
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