[R] how can I get the coefficients of x^0, x^1, x^2, . , x^6 from expansion of (1+x+x^2)^3

[Gabor Grothendieck]

From:   Peter Yang <peterwyang at gmail.com>

>I would like to get the coefficients of x^0, x^1, x^2, . , x^6 from
>expansion of (1+x+x^2)^3.


# modification of DD in example(D) to support 0th derivative
DD <- function(expr,name, order = 0) {
   if(order == 0) 
	expr
   else DD(D(expr, name), name, order - 1)
}

# take symbolic derivatives, evaluate at 0 and divide by factorial n
sapply(0:6, function(i) eval(DD(e,"x",i),list(x=0)))/factorial(0:6)