>>>> "Martin Henry H. Stevens" <[EMAIL PROTECTED]> 10/20/05 08:47AM >>> >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$country=="MX" ] <- "NoAm" A shorter alternative to the above is to use %in% like: mydata$continent[ mydata$country %in% c("US","CA","MX") ] <- "NoAm" You could also create a new data frame with 2 columns for the country and corresponding continent, then merge this with your data (see ?merge). > >#Repeat for all countries and continents. > >Hank > > >On Oct 19, 2005, at 8:09 PM, Avram Aelony wrote: > >> Hello, >> >> I have read through the manuals and can't seem to find an answer. >> >> I have a categorical, character variable that has hundreds of >> values. I want to group the existing values of this variable into >> a new, derived (categorical) variable by applying conditions to the >> values in the data. >> >> For example, suppose I have a data frame with variables: date, >> country, x, y, and z. >> >> x,y,z are numeric and country is a 2-digit character string. I >> want to create a new derived variable named "continent" that would >> also exist in the data frame. The Continent variable would have >> values of "Asia", "Europe", "North America", etc... >> >> How would this best be done for a large dataset (>10MB) ? >> I have tried many variations on following without success (note in >> a real example I would have a longer list of countries and >> continent values): >> >> >>> mydata$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 > Greg Snow, Ph.D. Statistical Data Center, LDS Hospital Intermountain Health Care [EMAIL PROTECTED] (801) 408-8111 ______________________________________________ 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