47 lines
1.3 KiB
R
47 lines
1.3 KiB
R
|
#!/usr/bin/env r
|
||
|
|
|
||
|
|
## this short example was provided in response to this StackOverflow questions:
|
||
|
|
## http://stackoverflow.com/questions/6807068/why-is-my-recursive-function-so-slow-in-r
|
||
|
|
## and illustrates that recursive function calls are a) really expensive in R and b) not
|
||
|
|
## all expensive in C++ (my machine sees a 700-fold speed increase) and c) the byte
|
||
|
|
## compiler in R does not help here.
|
||
|
|
|
||
|
|
suppressMessages(library(Rcpp))
|
||
|
|
|
||
|
|
## byte compiler
|
||
|
|
require(compiler)
|
||
|
|
|
||
|
|
## A C++ version compile with cppFunction
|
||
|
|
fibRcpp <- cppFunction( '
|
||
|
|
int fibonacci(const int x) {
|
||
|
|
if (x == 0) return(0);
|
||
|
|
if (x == 1) return(1);
|
||
|
|
return (fibonacci(x - 1)) + fibonacci(x - 2);
|
||
|
|
}
|
||
|
|
' )
|
||
|
|
|
||
|
|
|
||
|
|
## for comparison, the original (but repaired with 0/1 offsets)
|
||
|
|
fibR <- function(seq) {
|
||
|
|
if (seq == 0) return(0);
|
||
|
|
if (seq == 1) return(1);
|
||
|
|
return (fibR(seq - 1) + fibR(seq - 2));
|
||
|
|
}
|
||
|
|
|
||
|
|
## also use byte-compiled R function
|
||
|
|
fibRC <- cmpfun(fibR)
|
||
|
|
|
||
|
|
## load rbenchmark to compare
|
||
|
|
library(rbenchmark)
|
||
|
|
|
||
|
|
N <- 35 ## same parameter as original post
|
||
|
|
res <- benchmark(fibR(N),
|
||
|
|
fibRC(N),
|
||
|
|
fibRcpp(N),
|
||
|
|
columns=c("test", "replications", "elapsed",
|
||
|
|
"relative", "user.self", "sys.self"),
|
||
|
|
order="relative",
|
||
|
|
replications=1)
|
||
|
|
print(res) ## show result
|
||
|
|
|