Recursive manipulation of vector elements

Question

I have a vector a and want to multiply each element recursively with b, without using a loop.

a <- rep(0, 10)
a[1] <- 1
b <         


        

Answer 1

The exponent function ^ is vectorized, so quite simply:

2^(0:9)
# [1]   1   2   4   8  16  32  64 128 256 512

which you might also want to write

2^seq(from=0, to=9)

For long vectors, I am pretty sure @JoshuaUlrich's method will be much faster, but this one is certainly very compact. You also said you were not particularly concerned about speed.