Aurélien PHILIPPOT wrote > > 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@ 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. >
One way would be to use the aggregate function. # Your Data ... # Note: I have removed the quotes off the output variable x 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) # Aggregate Function aggregate(df$x, by=list(df$comn,df$mi),FUN=sd) HTH Pete -- View this message in context: http://r.789695.n4.nabble.com/Group-several-variables-and-apply-a-function-to-the-group-tp4158017p4158090.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.