thanks everybody!

On Wed, Aug 31, 2011 at 5:03 AM, jim holtman <jholtman@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 <govokai@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]]

