Brilliant, Dirk. Thanks for that.
Next time, I'll read the Rcpp Sugar .pdf more carefully.
Cheers,
On 13/04/11 12:43, Dirk Eddelbuettel wrote:
On 13 April 2011 at 12:19, Cedric Ginestet wrote:
| Hi guys,
|
| I want to produce discrete uniform variates within C++ from the runif()
| function available through Rcpp Sugar. However, I don't seem to be able to
find
| the appropriate cast in order to return an IntegerVector as opposed to a
| numeric one. I have naively used int(), but this is clearly not sufficient.
|
| Any help would be greatly appreciated,
| Ced
|
| ##########################################
| #### Discrete uniform variate.
| src<- '
| using namespace Rcpp ;
| RNGScope scope;
| int n = as<int>(xn);
| int a = as<int>(xa);
| int b = as<int>(xb);
| IntegerVector vec(n);
| for(int i=0; i<n; ++i) vec[i] = (int)floor(runif(i,a,b));
| return vec;'
| cxxfun<- cxxfunction(sig=signature(xn="numeric",xa="numeric",xb=
| "numeric"),body=src,plugin="Rcpp",verbose=TRUE)
| cxxfun(10,0,10);
|
| ##########################
| Error in compileCode(f, code, language = language, verbose = verbose) :
| Compilation ERROR, function(s)/method(s) not created! file52d217df.cpp: In
| function ?SEXPREC* file52d217df(SEXPREC*, SEXPREC*, SEXPREC*)?:
| file52d217df.cpp:37: error: invalid cast from type ?Rcpp::sugar::SugarMath_1
|<true, double, double, Rcpp::Vector<14>, double (*)(double)>? to type ?int?
| make: *** [file52d217df.o] Error 1
| ##################################################
Well as a start maybe try this as your loop:
for (int i=0; i<n; ++i) {
double tmp = runif(1,a,b)); // why where you using i here?
vec[i] = static_cast<int>(tmp); // C++ static cast
}
But you do of course understand that
a) Rcpp sugar can draw an entire vector at once and
b) Rcpp sugar also has a vectorised floor() function
right? So with that try
R> src<- '
+ RNGScope scope;
+ int n = as<int>(xn);
+ int a = as<int>(xa);
+ int b = as<int>(xb);
+ IntegerVector vec(n);
+ vec = floor(runif(n,a,b));
+ return vec;'
R> cxxfun<- cxxfunction(sig=signature(xn="numeric",xa="numeric",xb="numeric"),
+ body=src,plugin="Rcpp")
R> cxxfun(10,0,10);
[1] 8 5 1 7 0 0 6 9 8 1
R>
Hth, Dirk
| --
| Cedric Ginestet
| Centre for Neuroimaging Sciences (L3.04)
| NIHR Biomedical Research Centre
| Department of Neuroimaging
| Institute of Psychiatry, Box P089
| King's College London
| De Crespigny Park
| London
| SE5 8AF
|
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