According to my understanding, the setdiff() function analyses two vectors and returns the elements that are present in one vector but absent in the other. Given these vectors, if that's the case, then...
item 1 - c (1,2,3)
thing2 <- c(2,3,4)\sthing3 <- c(1,2,3)\s...my here's results.
SetDifference(Thing1,Thing2) >  1
SetDifference(Thing2,Thing3) >  4
SetDifference(Thing1,Thing3) > Numeric (0)
Shouldn't comparing item 1 and item 2 yield the same results as comparing item 2 and item 3? How can we get a symmetric set difference result that looks like a "outer join" such that we can see all the elements that would be missing if we unioned thing1 and thing2? I would value data more than I would like to know R's functionality. tables move closer. I believe that setdiff() analyses two vectors and outputs the elements that are present in one vector but absent in the other.