[R] Grouping data in dataframe

[Peter Alspach]

Tena koe Timo

?aggregate

HTH ...

Peter Alspach 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Timo Schneider
> Sent: Wednesday, 15 July 2009 3:56 p.m.
> To: r-help at r-project.org
> Subject: [R] Grouping data in dataframe
> 
> 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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> 

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