Nothing
#!/usr/bin/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.
## inline to compile, load and link the C++ code
require(inline)
## byte compiler
require(compiler)
## we need a pure C/C++ function as the generated function
## will have a random identifier at the C++ level preventing
## us from direct recursive calls
incltxt <- '
int fibonacci(const int x) {
if (x == 0) return(0);
if (x == 1) return(1);
return (fibonacci(x - 1)) + fibonacci(x - 2);
}'
## now use the snipped above as well as one argument conversion
## in as well as out to provide Fibonacci numbers via C++
fibRcpp <- cxxfunction(signature(xs="int"),
plugin="Rcpp",
incl=incltxt,
body='
int x = Rcpp::as<int>(xs);
return Rcpp::wrap( fibonacci(x) );
')
## 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
Any scripts or data that you put into this service are public.
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.