[R] extracting submatrix from a bigger one

[Bert Gunter]

Oh yes, that's even better!

-- Bert

On Mon, Jun 24, 2013 at 10:33 AM, Rui Barradas <ruipbarradas at sapo.pt> wrote:
> 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
>>>>
>>>> ______________________________________________
>>>> 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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