[R] data normalization

[arun]

Hi,

Probably you might have got the solution.


Anyway, you can try this:
Dat <- read.table(text="
ID  TIME    DV
1  0  0.880146038
1  1  0.88669051
1  3  0.610784702
1  5  0.756046666
2  0  0.456263368
2  1  0.369991537
2  3  0.508798346
2  5  0.441037014
3  0  0.854905349
3  1  0.960457553
3  3  0.609434409
3  5  0.655006334
",sep="", header = TRUE)



 SpDV<-function(x,n) split(x,sort(rank(x) %%n))
 DVlist<-SpDV(Dat$DV,length(unique(Dat$ID)))
 Dat$DVn<-cbind(unlist(lapply(DVlist,FUN=function(x) x/x[1])))
> Dat
   ID TIME        DV       DVn
1   1    0 0.8801460 1.0000000
2   1    1 0.8866905 1.0074357
3   1    3 0.6107847 0.6939584
4   1    5 0.7560467 0.8590014
5   2    0 0.4562634 1.0000000
6   2    1 0.3699915 0.8109166
7   2    3 0.5087983 1.1151418
8   2    5 0.4410370 0.9666281
9   3    0 0.8549053 1.0000000
10  3    1 0.9604576 1.1234665
11  3    3 0.6094344 0.7128677
12  3    5 0.6550063 0.7661741


A.K.



----- Original Message -----
From: york8866 <yu_york at hotmail.com>
To: r-help at r-project.org
Cc: 
Sent: Tuesday, June 19, 2012 8:08 PM
Subject: [R] data normalization

I have a dataframe such like the following:

ID    TIME    DV
1    0    0.880146038
1    1    0.88669051
1    3    0.610784702
1    5    0.756046666
2    0    0.456263368
2    1    0.369991537
2    3    0.508798346
2    5    0.441037014
3    0    0.854905349
3    1    0.960457553
3    3    0.609434409
3    5    0.655006334
.    .    .
.    .    .


I would like to generate another column with the normalized values of DV.
for each ID, normalize to the value at TIME 0.  
I was able to use 2 loops to do the normalization, however, as 2 loops took
a long time for the calculation, I don't know whether there's a better way
to do it. 
I have the following code with only 1 loop, but it did not work.  Can anyone
help with this? Thanks,

IDS <- unique(data.frame$ID)
for(WhichID in IDS) 
{
subset <- data.frame[,"ID"] == WhichID
DVREAL <- data.frame[subset,"DV"]
DVNORM[WhichID] <- DVREAL/DVREAL[1]
}







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