extracting submatrix from a bigger one

Hello,

I had forgotten the much simpler solutions. The following should do it.

split(dataset, dataset$ID)


Rui Barradas

Em 24-06-2013 18:13, Bert Gunter escreveu:

First of all, is your data structure a matrix or a data frame? They
are different!

Assuming the latter, a shorter version of Rui's answer that avoids
unique() and automatically takes care of names is:

result <- by(dataset, dataset$ID,I)

See ?by, ?tapply, and ?split

-- Bert

On Mon, Jun 24, 2013 at 9:24 AM, Rui Barradas <ruipbarradas at sapo.pt>
wrote:

Hello,

Try the following.


result <- lapply(unique(dataset$ID), function(uid) dataset[dataset$ID ==
uid, ])
names(result) <- unique(dataset$ID)


Hope this helps,

Rui Barradas

Em 24-06-2013 15:36, matteo escreveu:

Hi guys,
I'm a newby, so sorry for the easy question.

I have a matrix (459x28) in which a large number of observations are
repeated (same placed sampled in different times).
One of the columns is refers to the ID of the place of sampling.
What I would like is to extract subset matrix for every point of
sampling.

I can do it manually, e.g. x1<-data.frame(dataset[dataset$ID=="x1",])
but is it possible to write a script and let do it to R?
So i got n submatrix of the n ID found in the original columns.

Cheers

Matteo