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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