[R] Calculating SD according to groups of rows
dieter.menne at menne-biomed.de
Thu Nov 20 09:20:36 CET 2008
pufftissue pufftissue <pufftissue <at> gmail.com> writes:
> What I am getting is indeed:
> 7200 23955 34563 8934
> 16.39977 10.03896 11.234 14.02
> I'd like the final output to be:
> subject_id hr_Stand_Deviation
> 7200 16.39977
> 23955 10.03896
> 34563 11.234
> 8934 14.02
The hard way could go like that; I personally got used to it, but I admit
it is one of the thinks that are unusually difficult in R.
dat = data.frame(SUBJECT_ID=sample(letters[1:5],100,TRUE),HR=rnorm(100))
sd.list = with(dat, tapply(HR, SUBJECT_ID, sd))
I think Hadley Wickham tried to make life easier with the plyr package,
so I thought something like the below would work out of the box.
However, there must be something wrong with the syntax, the
result is only "approximately" correct.
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