thanks everybody!
On Wed, Aug 31, 2011 at 5:03 AM, jim holtman <jholt...@gmail.com> wrote:
> You can use data.table:
>
> > group <- c(rep('A', 8), rep('B', 15), rep('C', 6))
> > time <- c(rep(seq(1:4), 2), rep(seq(1:5), 3), rep(seq(1:3), 2))
> > value <- runif (29, 1, 10)
> > dfx <- data.frame (group, time, value)
> > require(data.table)
> > dfx <- data.table(dfx)
> > dfx[,
> + list(mean = mean(value), sd = sd(value))
> + , by = list(group, time)
> + ]
> group time mean sd
> [1,] A 1 7.902432 0.8484807
> [2,] A 2 5.583566 1.1996167
> [3,] A 3 3.412691 1.1138794
> [4,] A 4 7.786522 2.2367483
> [5,] B 1 6.669257 2.1476769
> [6,] B 2 2.902291 1.6630821
> [7,] B 3 6.913593 0.9110182
> [8,] B 4 4.713124 0.9521689
> [9,] B 5 7.285824 1.5884689
> [10,] C 1 3.799665 3.7728015
> [11,] C 2 9.218785 0.9415034
> [12,] C 3 5.098077 3.5256497
>
>
> On Wed, Aug 31, 2011 at 4:19 AM, Kai Megerle <govo...@gmail.com> wrote:
> > Hi all,
> > I apologize for this probably stupid question, but I really can't figure
> it
> > out.
> > I have a dataframe like this:
> >
> > group <- c(rep('A', 8), rep('B', 15), rep('C', 6))
> > time <- c(rep(seq(1:4), 2), rep(seq(1:5), 3), rep(seq(1:3), 2))
> > value <- runif (29, 1, 10)
> > dfx <- data.frame (group, time, value)
> >
> > I want to calculate mean and standard deviation for all values that
> belong
> > to the same group and the same time and end up with a dataframe with the
> > columns time, group, mean and sd that contains the calculated values for
> > every group at every time point only once (12).
> > What is the most elegant way to do this? Oh, and I would like to avoid
> > renaming columns (like the _X1/_X2 created by casting with multiple
> > functions), if possible.
> > I am sure that this is pretty basic, but I have already wasted a
> ridiculous
> > amount of time on this.
> >
> > Thanks,
> >
> > Kai
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
>
> --
> Jim Holtman
> Data Munger Guru
>
> What is the problem that you are trying to solve?
>
[[alternative HTML version deleted]]
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