[R] rank(x,y)?

[Duncan Murdoch]

Suppose I have two columns, x,y.  I can use order(x,y) to calculate a 
permutation that puts them into increasing order of x,
with ties broken by y.

I'd like instead to calculate the rank of each pair under the same 
ordering, but the rank() function doesn't take multiple values
as input.  Is there a simple way to get what I want?

E.g.

 > x <- c(1,2,3,4,1,2,3,4)
 > y <- c(1,2,3,1,2,3,1,2)
 > rank(x+y/10)
[1] 1 3 6 7 2 4 5 8

gives me the answer I want, but only because I know the range of y and 
the size of gaps in the x values.  What do I do in general?

Duncan Murdoch