How to concatenate two or more vectors in Amardillo?

Question

For example, if I have

vec a(3, fill::randu);
vec b(5, fill::randu);

How can I get a new vector c of size 8, where the first three elements are from a and the rest from b?

Answer 1

You can use join_cols(a,b) since vec inherits from mat

#include<armadillo>
using namespace arma;
int main()
{
     vec a(3, fill::randu);
     vec b(5, fill::randu);
     vec c;

     c = join_cols(a,b);
     a.print("a");
     b.print("b");
     c.print("a..b"); 
    return 0;
}

...gives the output

a
   0.8402
   0.3944
   0.7831
b
   0.7984
   0.9116
   0.1976
   0.3352
   0.7682
a..b
   0.8402
   0.3944
   0.7831
   0.7984
   0.9116
   0.1976
   0.3352
   0.7682