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 <aurelien.philip...@gmail.com> >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]]
______________________________________________ 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.