[R] Finding a single unique item in duplicated vectors

[John Kane]

I have a very simple problem and am completely missing
the solution.
I have two character variables (character ID's from
two datasets) Data set 'b'
is data set 'a' with one more subject added.
How do I find out which is the added subject?

I have tried duplicated and unique without much
success.  I can find all the
duplicated ID's but how do I extract the new "unique"
one?
Example:
a  <-  as.character(Cs(b,d,c,a))
b  <- as.character( Cs(a,b,c,d,e))
h  <- c(a,b) ; h
h[duplicated(h)]

I just want to extract that "e"! 

I had thought that
h[!duplicated(h)]
might work but it simply returns all the unique values
whereas
I simply want to simply find the odd man out.

I thought of using sorting the vectors & using a cbind
but the id's are assigned
more or less randomly so that didn't work.
 
 Thanks