[R] Centering data frame by factor

[David Winsemius]

On Jul 19, 2011, at 4:50 AM, Daniel Malter wrote:

>
> P1-tapply(P1,Experiment,mean)[Experiment]

Another way would be with ave(), but I discovered that it does not  
accept subsidiary arguments and does not issue warnings either, so  
this works:

 >  with(dfrm, ave(P1, Experiment, FUN=function(x) scale(x,   
scale=FALSE) ) )
[1] -2  0  2  1 -1  0


But this doesn't behave "as directed" ... by my pre-operational R-brain.

with(dfrm, ave(P1, Experiment, FUN=scale,  scale=FALSE) )
[1] -1  0  1  1 -1  0

(It applies both default arguments and issues no warning about unused  
argument. Most (well, some anyway) functions like this accept  
subsidiary arguments with ..., but `ave` uses that construction to  
gather its factor arguments rather than expecting them to be in a list  
or vector, as do tapply, aggregate, and by. Some functions like mapply  
and many other give you a moreArgs option, but not ave.)

-- 
David.

>
> HTH,
> Daniel
>
>
> ronny wrote:
>>
>> Hi,
>>
>> I would like to center P1 and P2 of the following data frame by the  
>> factor
>> "Experiment", i.e. substruct from each value the average of its
>> experiment, and keep the original data structure, i.e. the  
>> experiment and
>> the group of each value.
>>
>> RAW=
>> data 
>> .frame 
>> ("Experiment 
>> "= 
>> c 
>> (2,2,2,1,1,1 
>> ),"Group 
>> "= 
>> c 
>> ("A 
>> ","A","B","A","A","B"),"P1"=c(10,12,14,5,3,4),"P2"=c(8,12,16,2,3,4))
>>
>> Desired result:
>>
>> NORMALIZED=
>> data 
>> .frame 
>> ("Experiment 
>> "= 
>> c 
>> (2,2,2,1,1,1 
>> ),"Group 
>> "= 
>> c 
>> ("B 
>> ","A","B","B","A","B"),"P1"=c(-2,0,2,1,-1,0),"P2"=c(-4,0,4,-1,0,1))
>>
>> I tried using "by", but then I lose the original order, and the  
>> "Group"
>> varaible. Can you help?
>>
>>> RAW
>>  Experiment Group P1 P2
>>         2     A 10  8
>>         2     A 12 12
>>         2     B 14 16
>>         1     A  5  2
>>         1     A  3  3
>>         1     B  4  4
>>
>> NOT.OK<- within (RAW,
>> {P1<-do.call(rbind,by(RAW$P1,RAW$Experiment,scale,scale=F))})
>>
>>> NOT.OK
>>  Experiment Group P1 P2
>>          2     A  1  8
>>          2     A -1 12
>>          2     B  0 16
>>          1     A -2  2
>>          1     A  0  3
>>          1     B  2  4
>>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Centering-data-frame-by-factor-tp3677609p3677620.html
> Sent from the R help mailing list archive at Nabble.com.
>
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David Winsemius, MD
West Hartford, CT