Dear All, I have a data frame (mydata), with let say 5 columns V1,V2,...,V5. (we know the power set of {V1,V2,..,V5} has 2^5-1 elements). I need to construct a vector T of length 5 which its i-th element is the maximum of (let say) mean values obtained based on the columns subset of size i. (MY FUNCTION TO APPLY ON COLUMNS SUBSET IS NOT SO SIMPLE AS MEAN AND I WILL REPLACE IT.) I mean: T[1]=max(mean(mydata[,1]),...,mean(mydata[,5])) T[2]=max(mean(mydata[,c(1,2)],mean(mydata[,c(1,3)],...,mean(mydata[,c(1,5]) T[3]=max(mean(mydata[,c(1,2,3)],mean(mydata[,c(1,2,4)],...,mean(mydata[,c(3,4,5)]) .... T[5]=max(mean(mydata[,c(1,2,3,4,5)] Many thanks in advance. Hamid