[R] extracting submatrix from a bigger one

[Bert Gunter]

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
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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