[R] data normalization

[Dimitris Rizopoulos]

assuming that the entries for each subject are ordered with respect to 
TIME and each subject has a measurement at TIME = 0, then you could use 
the following:

Data <- read.table(textConnection("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"), header = TRUE)
closeAllConnections()

Data$DVn <- with(Data, ave(DV, ID, FUN = function (x) x/x[1]))
Data

If either of the above assumptions doesn't hold, you'll have to tweak it.


I hope it helps.

Best,
Dimitris


On 6/20/2012 2:08 AM, york8866 wrote:
> 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]
> }
>
>
>
>
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/data-normalization-tp4633911.html
> Sent from the R help mailing list archive at Nabble.com.
>
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>

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
Web: http://www.erasmusmc.nl/biostatistiek/