Vectorize a product calculation which depends on previous elements?

Question

I\'m trying to speed up/vectorize some calculations in a time series. Can I vectorize a calculation in a for loop which can depend on results from an earlier iteration? For

Answer 1

There is a function that does this particular calculation: cumprod (cumulative product)

> cumprod(z[zi])
[1] 1 0 0 0 0

> cumprod(c(1,2,3,4,0,5))
[1]  1  2  6 24  0  0

Otherwise, vectorize with Rccp as other answers have shown.