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

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