exactly like that!
thanks a lot.
Aurelien
2011/12/4 Felipe Carrillo
> Like this?
> library(plyr)
> ddply(df,.(comn,mi),summarise,stDEV=sd(x))
>
> Felipe D. Carrillo
> Supervisory Fishery Biologist
> Department of the Interior
> US Fish & Wildlife Service
> California, USA
> http://www.fws.gov/redbluff/rbdd_jsmp.aspx
>
> *From:* Aurélien PHILIPPOT
> *To:* R-help@r-project.org
> *Sent:* Sunday, December 4, 2011 12:32 PM
> *Subject:* [R] Group several variables and apply a function to the group
>
> Dear R-experts,
> I am struggling with the following problem, and I am looking for advice
> from more experienced R-users: I have a data frame with 2 identifying
> variables (comn and mi), and an output variable (x). comn is a variable for
> a company and mi is a variable for a month.
>
> comn<-c("abc", "abc", "abc", "abc", "abc", "abc", "xyz", "xyz","xyz",
> "xyz")
> mi<- c("1", "1","1", "2", "2", "2", "1", "1", "3", "3")
> x<- c("-0.0031", "0.0009", "-0.007", "0.1929","0.0087", "0.099","-0.089",
> "0.005", "-0.0078", "0.67" )
> df<- data.frame(comn=comn, mi=mi, x=x)
>
>
> For each company, within a particular month, I would like to compute the
> standard deviation of x: for example, for abc, I would like to compute the
> sd of x for month1 (when mi=1) and for month2 (when mi=2).
>
> In other languages (Stata for instance), I would create a grouping variable
> (group comnn and mi) and then, apply the sd function for each group.
>
> However, I don't find an elegant way to do the same in R:
>
> I was thinking about the following: I could subset my data frame by mi and
> create one file per month, and then make a loop and in each file, use a
> "by" operator for each comn. I am sure it would work, but I feel that it
> would be like killing an ant with a tank.
>
> I was wondering if anyone knew a more straightforward way to implement that
> kind of operation?
>
> Thanks a lot,
>
> Best,
> Aurelien
>
> [[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.
>
>
>
[[alternative HTML version deleted]]