Hi, I have a question, explained by the following example: > a<-c(1,2,3) > b<-c(1,1,2,4) > b[match(a,b, nomatch=0)] [1] 1 2 which means it returns "the first match", but I want to get 1 1 2 instead of 1 2 In a word, how to do multiple matching? thanks, -- Weiwei Shi, Ph.D "Did you always know?" "No, I did not. But I believed..." ---Matrix III