I believe this will generalize. But check carefully! Using your example (Excellent!), use ave():
with(df,ave(seq_along(var1),var2,FUN=function(i) var3[i]/var3[i][var1[i]=="c"])) [1] 0.5000000 1.0000000 1.0000000 0.8333333 0.3333333 1.0000000 1.7500000 [8] 1.0000000 1.0000000 This is kind of a low level brute force approach. Others may have more elegant approaches. -- Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." H. Gilbert Welch On Wed, Mar 26, 2014 at 9:09 AM, Johannes Radinger <johannesradin...@gmail.com> wrote: > Hi, > > I have data in a dataframe in following structure > var1 <- c("a","b","c","a","b","c","a","b","c") > var2 <- c("X","X","X","Y","Y","Y","Z","Z","Z") > var3 <- c(1,2,2,5,2,6,7,4,4) > df <- data.frame(var1,var2,var3) > > Now I'd like to calculate relative values of var3. This values > should be relative to the base value (where var1=c) which is > indicated for each group (var2). > > To illustrate how my result column should look like I divide > the column var3 by a vector c(2,2,2,6,6,6,4,4,4) (= for each group > of var2 the value c) > > Of course this can also be done like this: > df$div <- rep(df$var3[df$var1=="c"],each=length(unique(df$var1))) > df$result_calc <- df$var3/df$div > > > However what when the dataframe is not as simple and not that well ordered > as > in the example here. So for example there is always a value c for each group > but all the "c"s are clumped in the last rows of the dataframe or scatterd > in a random > mannar. Is there a simple way to still calculate such relative values. > Probably with an approach using apply, but maybe someone can give me a hint. > Or do I need to sort my dataframe in order to do such calculations? > > best, > > /Johannes > > [[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. ______________________________________________ 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.