[R] : reshape/aggregate

[Petr PIKAL]

Hi

> The plyr solution is:
> 
> library(plyr)
> ddply(dfx,  .(group, time), summarize, mean = mean(value), sd = 
sd(value))

I tried to do the task by ddply but I had difficulties to understand the 
correct syntax. Maybe in next issue of plyr summarise could be referenced 
in ddply help page.

Or add something like:

When performing summary values for a data frame according to levels of a 
factor you shall use syntax
ddply(.data, .variables, summarise, .fun, ...)

Regards
Petr


> 
> Best,
> Ista
> 
> On Wed, Aug 31, 2011 at 7:13 AM, Petr PIKAL <petr.pikal at precheza.cz> 
wrote:
> > Hi
> >
> >> 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.
> >
> > see
> > ?aggregate
> >
> > aggregate(dfx$value, list(group=dfx$group, time=dfx$time), function(x)
> > c(mean(x), sd(x)))
> >
> > and maybe also plyr package could help you
> >
> > Regards
> > Petr
> >
> >
> >>
> >> Thanks,
> >>
> >> Kai
> >>
> >>    [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
> >> R-help at 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.
> >
> > ______________________________________________
> > R-help at 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.
> >
> 
> 
> 
> -- 
> Ista Zahn
> Graduate student
> University of Rochester
> Department of Clinical and Social Psychology
> http://yourpsyche.org