Rcpp Copy a vector to a vector

c++, copy, rcpp, vector

Solution

As hinted in the comment, you could use

Grp1 = clone(Grp2) ;

but this will create a new R object that then get assigned to `Grp1`, so you pay for some memory allocation and you discard some memory that could have been used, i.e. more work for the garbage collector down the line.

You could also just reuse the existing memory from `Grp1` with std::copy

std::copy( Grp2.begin(), Grp2.end(), Grp1.begin() ) ;

Another way that is perhaps over the top is to use `sapply`. Something like this:

auto identity = [](double x){ return x; } ;
Grp1 = sapply( Grp2, identity );

But given `Rcpp` does not sapply over lambdas, you'd probably have to define `identity` outside your function for this approach to be useable.

inline double identity(double x){ 
    return x ;
}

FWIW, in `Rcpp14` or `Rcpp11`, you could simply do:

Grp1 = import(Grp2) ;

Problem

I am new to Rcpp and C++ coding in general, so forgive me for asking basic questions. The cpp part of the code is ``` // test.cpp #include <Rcpp.h> using namespace Rcpp; // [[Rcpp::export]] void testRun() { IntegerVector Grp1 = IntegerVector::create(1,2,3,4); IntegerVector Grp2 = IntegerVector::create(3,4,5,6); Rf_PrintValue(Grp1); Grp1 = Grp2; Rf_PrintValue(Grp1); Grp2[3] = Grp2[3]+1; Rf_PrintValue(Grp1); } ``` and when I run testrun(), I get the output ``` > Rcpp::sourceCpp('test.cpp') > testRun() [1] 1 2 3 4 [1] 3 4 5 6 [1] 3 4 5 7 ``` When I assign `Gr2` to `Gr1` in `Gr1 = Gr2`, changing elements in `Gr2` after the assignment changes the values in `Gr1` as well. Is there a function for IntegerVectors that could do something like `Gr1 = copy of Gr2` or should I be using a loop to do that. Thanks a lot!

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