Avoid two for loops in R

Question

I have a R code that can do convolution of two functions...

convolveSlow <- function(x, y) {  
nx <- length(x); ny <- length(y)  
xy <- numeric(nx          


        

Answer 1

The convolveFast function can be optimized a little by carefully using integer math only and replacing (1:ny)-1L with seq.int(0L, ny-1L):

convolveFaster <- function(x, y) {
    nx <- length(x)
    ny <- length(y)
    xy <- nx + ny - 1L
    xy <- rep(0L, xy)
    for(i in seq_len(nx)){
        j <- seq_len(ny)
        ij <- i + j - 1L
        xy[i+seq.int(0L, ny-1L)] <- xy[ij] + x[i] * y
    }
    xy
}