[R] readMat - how to retrieve the variables

[David Winsemius]

On Mar 13, 2011, at 6:42 PM, Eduardo M. A. M.Mendes wrote:

>
> Hi Joshua
>
> Many thanks.
>
> The values of flow can be accessed in a weird way and we can used  
> them for some calculations.  Since I am a newbie as far as using R  
> is concerned I wonder whether you could tell me how to create a  
> structure in R that looks like the one I have in matlab (that is, a  
> variable a that contains river1 and river2 that contains flow and  
> precipitation).

If you posted the results of dput(a) ,  we might be able to test our  
pet theories, but here is my hapless first guess:

mat.R.struc <- with(b$a[,,1],   #looks like it was a matrix that had  
lists as elements
              cbind(as.data.frame(river1), as.data.frame(river2) )
                 )

It's not so much that it will "look like" your Matlab structure, but  
it could be something that you can work with. This will create a long- 
format structure which is a typical one for plotting ans regression.  
Another option would be an R array which, unlike matrices, can have  
more than 2 dimensions.


>
> Cheers
>
> Ed
>
>
> -----Original Message-----
> From: Joshua Wiley [mailto:jwiley.psych at gmail.com]
> Sent: Sunday, March 13, 2011 7:20 PM
> To: Eduardo M. A. M.Mendes
> Cc: R-help at r-project.org
> Subject: Re: [R] readMat - how to retrieve the variables
>
> On Sun, Mar 13, 2011 at 2:56 PM, Eduardo M. A. M.Mendes <emammendes at gmail.com 
> > wrote:
>> Hi Joshua
>>
>> Many thanks for the prompt reply.
>>
>> I have saved a short version of the matlab file and the output on R  
>> is
>>
>>> b=readMat("testr.mat")
>>> b
>> $a
>> , , 1
>>
>>      [,1]
>> river1 List,2
>> river2 List,2
>
> It looks like you are dealing with a special series of lists nested  
> within three dimensional arrays within lists.  My suggestion would  
> be to double check that the matlab file has reasonable data  
> (whatever that means) and try to double check your use of readmat  
> (do you meet all the requirements for versions, etc.).  That is not  
> a common R structure so the extraction is similarly uncommon.   
> Perhaps Henrik will be along with more helpful answers.
>
> Good luck,
>
> Josh
>>
>>
>> attr(,"header")
>> attr(,"header")$description
>> [1] "MATLAB 5.0 MAT-file, Platform: PCWIN, Created on: Sun Mar 13  
>> 18:51:54 2011                                                  "
>>
>> attr(,"header")$version
>> [1] "5"
>>
>> attr(,"header")$endian
>> [1] "little"
>>
>> When I issue the command b$a[,,1]$river1[,,1]$flow  I see the flow  
>> values.
>>
>> Unfortunately the data is confidential.
>>
>> Many thanks
>>
>> Ed
>>
>>
>> -----Original Message-----
>> From: Joshua Wiley [mailto:jwiley.psych at gmail.com]
>> Sent: Sunday, March 13, 2011 6:30 PM
>> To: Eduardo M. A. M.Mendes
>> Cc: R-help at r-project.org
>> Subject: Re: [R] readMat - how to retrieve the variables
>>
>> Hi Ed,
>>
>> Can you please provide *at least* the R output from running:
>>
>> str(data)
>>
>> where "data" is the variable name you stored the results of  
>> readMat() in.  If it is reasonably small and can be sent as  
>> plaintext (I do not know Matlabs file format off hand), you could  
>> send us the actual data so we can try to read it in, but at the  
>> least str() will let us see how R is storing your data and give you  
>> some explanation.
>>
>> Side note, as data() is a function, it might be worthwhile to call  
>> your actual data something else (say, mydata, dat, etc.).  For  
>> anyone else interested, readMat() is in package "R.matlab".
>>
>> Cheers,
>>
>> Josh
>>
>> On Sun, Mar 13, 2011 at 2:07 PM, Eduardo M. A. M.Mendes <emammendes at gmail.com 
>> > wrote:
>>> Hello
>>>
>>> I have a matlab MAT file that contains one single variable: a.  The
>>> structure of a is as follows:
>>>
>>> a.river1.flow (flow values)
>>> a.river1.date_flow (date)
>>> a.river1.precip (precipitation values) a.river1.date_precip
>>> a.river2.flow a.river2.date_flow a.river2.precip  
>>> a.river2.date_precip
>>>
>>> I have used readMat to load the variable a in R, however I have no
>>> idea how readMat translates a.  I managed to get some values out of
>>> data=readMat("matfile.mat")
>>>
>>> data$a[,,1]$river1[,,1]$flow  -> Why do I need [,,1]?  Why not
>>> data$a$river1$flow?
>>>
>>> Many thanks
>>>
>>> Ed
>>>
>>> ______________________________________________
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>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>
> --
> Joshua Wiley
> Ph.D. Student, Health Psychology
> University of California, Los Angeles
> http://www.joshuawiley.com/
>
> ______________________________________________
> 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.

David Winsemius, MD
West Hartford, CT