Hi Avram- How many countries do you have? I would do it the following way because it is simple and I don't know any better, even if it is absurdly painstaking.
#Step 1 mydata$continent <- factor(NA, levels=c("NoAm","Euro")) #Steps 2 a-z mydata$continent[mydata$country=="US" | mydata$country=="CA" | mydata$country=="MX" ] <- "NoAm" #Repeat for all countries and continents. Hank On Oct 19, 2005, at 8:09 PM, Avram Aelony wrote: > Hello, > > I have read through the manuals and can't seem to find an answer. > > I have a categorical, character variable that has hundreds of > values. I want to group the existing values of this variable into > a new, derived (categorical) variable by applying conditions to the > values in the data. > > For example, suppose I have a data frame with variables: date, > country, x, y, and z. > > x,y,z are numeric and country is a 2-digit character string. I > want to create a new derived variable named "continent" that would > also exist in the data frame. The Continent variable would have > values of "Asia", "Europe", "North America", etc... > > How would this best be done for a large dataset (>10MB) ? > I have tried many variations on following without success (note in > a real example I would have a longer list of countries and > continent values): > > >> mydata$continent <- mydata[ mydata$country==list >> ('US','CA','MX'), ] -> "North America" >> > > I have read about factors, but I am not sure how they apply here. > > Can anyone help me with the syntax? I am sure it is trivial and a > common thing to do. > The ultimate goal is to compute percentages of x by continent. > > Thanks for any help in advance. > > -Avram > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting- > guide.html > Dr. Martin Henry H. Stevens, Assistant Professor 338 Pearson Hall Botany Department Miami University Oxford, OH 45056 Office: (513) 529-4206 Lab: (513) 529-4262 FAX: (513) 529-4243 http://www.cas.muohio.edu/~stevenmh/ http://www.muohio.edu/ecology/ http://www.muohio.edu/botany/ "E Pluribus Unum" ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html