[R] Grouping data in dataframe

[John Kane]

Another approach is to use the reshape package 

--Assuming your data.frame is called xx
------------------------------------------
libarary(reshape)
mm <- melt(xx, id=c("Size")) ; mm
cast(mm, Size ~variable, median)
--------------------------------------

--- On Tue, 7/14/09, Timo Schneider <timo.schneider at s2004.tu-chemnitz.de> wrote:

> From: Timo Schneider <timo.schneider at s2004.tu-chemnitz.de>
> Subject: [R] Grouping data in dataframe
> To: "r-help at r-project.org" <r-help at r-project.org>
> Received: Tuesday, July 14, 2009, 11:56 PM
> Hello,
> 
> I have a dataframe (obtained from read.table()) which looks
> like
> 
>  
>    ExpA   ExpB   ExpC   Size
> 1      12     23 
>   33      1
> 2      12     24 
>   29      1
> 3      10     22 
>   34      1
> 4      25     50 
>   60      2
> 5      24     53 
>   62      2
> 6      21     49 
>   61      2
> 
> now I want to take all rows that have the same value in the
> "Size"
> column and apply a function to the columns of these rows
> (for example
> median()). The result should be a new dataframe with the
> medians of the
> groups, like this:
> 
>  
>    ExpA   ExpB   ExpC   Size
> 1      12     23 
>   34      1
> 2      24     50 
>   61      2
> 
> I tried to play with the functions by() and tapply() but I
> didn't get
> the results I wanted so far, so any help on this would be
> great!
> 
> The reason why I am having this problem: (I explain this
> just to make
> sure I don't do something against the nature of R.)
> 
> I am doing 3 simillar experiments, A,B,C and I change a
> parameter in the
> experiment (size). Every experiment is done multiple times
> and I need
> the median or average over all experiments that are the
> same. Should I
> preprocess my data files so that they are completely
> different? Or is it
> fine the way it is and I just overlooked the simple
> solution to the
> problem described above?
> 
> Regards,
> Timo
> 
> ______________________________________________
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> and provide commented, minimal, self-contained,
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> 


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