借用这个想法comment https://stackoverflow.com/questions/29430726/vectorised-rcpp-random-binomial-draws/29432075#comment47035360_29432075作者:Romain Francois,关于我之前的 Rcpp 冒险之一,
func1 <- 'NumericMatrix mmult1(NumericMatrix a, NumericMatrix b) {
int acoln = a.ncol();
int bcoln = b.ncol();
NumericMatrix out = no_init_matrix(a.nrow(), acoln + bcoln);
for (int j = 0; j < acoln + bcoln; j++) {
if (j < acoln) {
out(_, j) = a(_, j);
} else {
out(_, j) = b(_, j - acoln);
}
}
return out;
}'
cppFunction(func1)
set.seed(42)
a <- matrix(rnorm(1e7), 1e3)
b <- matrix(runif(1e7), 1e3)
identical(mmult(a, b), mmult1(a, b))
#TRUE
library(microbenchmark)
microbenchmark(mmult(a, b),
mmult1(a, b),
cbind(a, b),
times = 10)
#Unit: milliseconds
# expr min lq mean median uq max neval
# mmult(a, b) 69.64 70.52 89.71 72.28 128.8 136.6 10
# mmult1(a, b) 50.84 50.95 69.65 51.43 111.6 114.4 10
# cbind(a, b) 192.35 194.67 201.13 195.30 196.1 255.9 10
没什么大不了的,但对于这样一个微不足道的改变来说也不错。