very simple subset selection in r

Question

Possible Duplicate:
How to remove rows of a matrix by row name, rather than numerical index?
removing elements in one vector from another in R

I have two vectors:

a<-c(1,2,3,4,5,6,7,8)
b<-c(7,3,6,4,8,1)

I would like to select those elements of a which are not in b

I tried subset(a, a!=b) but I get the warning:

longer object length is not a multiple of shorter object length

Answer 1

Try setdiff for vectors:

R> setdiff(a,b)
[1] 2 5

Answer 2

Try this:

a[!(a%in%b)]

Look at ?"%in%".