[R] group bunch of lines in a data.frame, an additional requirement

[Gabor Grothendieck]

See below.

On 9/13/06, Emmanuel Levy <emmanuel.levy at gmail.com> wrote:
> Thanks for pointing me out "aggregate", that works fine!
>
> There is one complication though: I have mixed types (numerical and character),
>
> So the matrix is of the form:
>
> A 1.0 200 ID1
> A 3.0 800 ID1
> A 2.0 200 ID1
> B 0.5 20   ID2
> B 0.9 50   ID2
> C 5.0 70   ID1
>
> One letter always has the same ID but one ID can be shared by many
> letters (like ID1)
>
> I just want to keep track of the ID, and get a matrix like:
>
> A 2.0 400 ID1
> B 0.7 35 ID2
> C 5.0 70 ID1
>
> Any idea on how to do that without a loop?

If V4 is a function of V1 then you can aggregate by it too and it will
appear but have no effect on the classification:

> aggregate(DF[2:3], DF[c(1,4)], mean)
  V1  V4  V2  V3
1  A ID1 2.0 400
2  C ID1 5.0  70
3  B ID2 0.7  35


>
>  Many thanks,
>
>     Emmanuel
>
> On 9/12/06, Emmanuel Levy <emmanuel.levy at gmail.com> wrote:
> > Hello,
> >
> > I'd like to group the lines of a matrix so that:
> > A 1.0 200
> > A 3.0 800
> > A 2.0 200
> > B 0.5 20
> > B 0.9 50
> > C 5.0 70
> >
> > Would give:
> > A 2.0 400
> > B 0.7 35
> > C 5.0 70
> >
> > So all lines corresponding to a letter (level), become a single line
> > where all the values of each column are averaged.
> >
> > I've done that with a loop but it doesn't sound right (it is very
> > slow). I imagine there is a
> > sort of "apply" shortcut but I can't figure it out.
> >
> > Please note that it is not exactly a matrix I'm using, the function
> > "typeof" tells me it's a list, however I access to it like it was a
> > matrix.
> >
> > Could someone help me with the right function to use, a help topic or
> > a piece of code?
> >
> > Thanks,
> >
> >   Emmanuel
> >
>
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