differentiating a numeric vector

Thanks for all the ideas.  splinefun looks like the simplest way to
achieve what I need:

x <- 1:10
y <- x^2
f <- splinefun(x,y)
f(3,deriv=0)

[1] 9

f(3,deriv=1)

[1] 6

f(3,2)

[1] 2

f(3,3)

[1] -3.330669e-16

The fda package has a function bsplineS which does nearly the same
thing, and the SemiPar solution looks good for irregular x and y
values, but the built-in function seems to work for my purposes.