Finding elements that do not overlap between two vectors

Question

I\'m trying to identify elements which are not included in the other vector. For instance in two vectors I have

list.a <- c(\"James\", \"Mary\", \"Jack\",         


        

Answer 1

An extended answer based on the comments from Hadley and myself: here's how to allow for duplicates.

Final Edit: I do not recommend anyone use this, because the result may not be what you expect. If there is a repeated value in x which is not in y, you will see that value repeated in the output. But: if, say, there are four 9s in x and one 9 in y, all the 9s will be removed. One might expect to retain three of them; that takes messier code.

mysetdiff<-function (x, y, multiple=FALSE) 
{
    x <- as.vector(x)
    y <- as.vector(y)
    if (length(x) || length(y)) {
        if (!multiple) {
             unique( x[match(x, y, 0L) == 0L])  
              }else  x[match(x, y, 0L) == 0L] 
        } else x
}

Rgames> x
[1]  8  9  6 10  9
Rgames> y
[1] 5 3 8 8 1
Rgames> setdiff(x,y)
[1]  9  6 10
Rgames> mysetdiff(x,y)
[1]  9  6 10
Rgames> mysetdiff(x,y,mult=T)
[1]  9  6 10  9
Rgames> mysetdiff(y,x,mult=T)
[1] 5 3 1
Rgames> setdiff(y,x)
[1] 5 3 1