[R] Using split and sapply to return entire lines

[Todd A. Gibson]

On Tue, Nov 08, 2005 at 10:47:26PM -0500, Gabor Grothendieck wrote:
> Also, one can use aggregate:
> 
> aggregate(DF[,-1], list(month = DF$month), max)

The issue here is that I need the row corresponding to the month with
the maximum length.  That is, aggregate(.) is returning both the
maximum month and maximum ratio for all rows with month=Jan.  I need
the single row in month=Jan which has the maximum length.

Thanks,
-TAG

> On 11/8/05, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> > Using package doBy at http://genetics.agrsci.dk/~sorenh/misc/index.html
> > try this:
> >
> > summaryBy(cbind(length, ratio, monthly1, monthly2) ~ month, DF, max)
> >
> >
> >
> > On 11/8/05, Todd A. Gibson <tgibson at augustcouncil.com> wrote:
> > > Hello,
> > > I have a data manipulation problem that I can easily resolve by using
> > > perl or python to pre-process the data, but I would prefer to do it
> > > directly in R.
> > >
> > > Given, for example:
> > >
> > >  month length ratio monthly1 monthly2
> > > 1 Jan   23     0.1   9        6
> > > 2 Jan   45     0.2   9        6
> > > 3 Jan   16     0.3   9        6
> > > 4 Feb   14     0.2   1        9
> > > 5 Mar   98     0.4   2        2
> > > 6 Mar   02     0.6   2        2
> > >
> > > (FWIW, monthly1 and monthly2 are unchanged for each month)
> > >
> > > I understand how to do aggregations on single fields using split and
> > > sapply, but how can I get entire lines.  For example, For the maximum
> > > of data$length grouped by data$month I would like to get back some
> > > form of:
> > >
> > > 2 Jan 45 0.2 9 6
> > > 4 Feb 14 0.2 1 9
> > > 5 Mar 98 0.4 2 2
> > >
> > > For mean, I would like to average all columns:
> > >
> > > Jan 28 0.2 9 6
> > > Feb 14 0.2 1 9
> > > Mar 50 0.5 2 2
> > >
> > > Thank you,
> > > -TAG
> > > Todd A. Gibson
> > >
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> >