[R] Odp: reshape/aggregate

[Ista Zahn]

The plyr solution is:

library(plyr)
ddply(dfx,  .(group, time), summarize, mean = mean(value), sd = sd(value))

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]]
>>
>> ______________________________________________
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>> 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