Dear All, here an example temp <- list(set1=c("a","b","d","x"), set2=c("b","c","q","m"), set3=c("b","f","e","k","q","h")) preserve only the first one string >temp set1 a b d x set2 c q m set3 f e k h OR remove repeated string >temp set1 a d x set2 c m set3 f e k h Thanks [[alternative HTML version deleted]]