[Rcpp-devel] What's the most efficient way to convert a NumericVector to an array of doubles

[Romain Francois]

Hello, 

just use: 

double* values = input.begin() ;

A NumericVector uses R allocated memory, and R allocates an array of doubles to store a numeric vector. 

You then need to remember you dońt own the pointer. So make sure your code does not eg delete[] it. 

The code you've used was very inefficient and will make many unecessary copies of the data, each time the std::vctor wants to grow. 

If you want a std:vector you can do something like this: 

std::vector<double> vec( input.begin(), input.end() ) ; 

Or: 

std::vector<double> vec = as< std::vector<double> >(input) ;

Romain

Le 29 juin 2013 à 12:08, Anwar Ludin <anwar.ludin at riskcetera.com> a écrit :

> Hello,
> 
> I need to interface some R code with a numerical library containing functions taking as input double*
> 
> What is the most efficient way to create an array of doubles from a NumericVector.
> 
> I was thinking of something like:
> 
> 
> 
> 
> 
> 
> // input is of type Rcpp::NumericVector and passed from R
> std::vector<double> vec;
> std::copy(input.begin(), input.end(), std::back_inserter(vec));
> 
> double* values = &vec[0];
> 
> // now call function taking a double*
> 
> 
> Regards,
> 
> Anwar
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