[R] data normalization

[york8866]

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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