Howto create combinations of several vectors without hardcoding loops in C++?

Question

I have several data that looks like this:

Vector1_elements = T,C,A
Vector2_elements = C,G,A
Vector3_elements = C,G,T
..... up to ...
VectorK_elements = ...

         


        

Answer 1

A C++0x solution. Provided, of course, your compiled supports it (currently GCC 4.5 and VS2010, I think).

The following compiles and works with GCC 4.5 using -std=c++0x switch. The use of variadic templates makes it possible to combine arbitrary number of containers. I am sure you can come up with a more idiomatic solution.

#include        
#include 
#include 
#include 
#include 

typedef std::vector myvec;

// Base case.
void combine2(const std::string &row) {
    std::cout << row << std::endl;
}

// Recursive variadic template core function.
template
void combine2(const std::string &row, const T0& cont0, T...cont_rest) {
    for (auto i = cont0.begin(); i != cont0.end(); ++i) {
        std::stringstream ss;
        ss << row << *i;
        combine2(ss.str(), cont_rest...);
    }
}

// The actual function to call.
template
void combine(T...containers) {
    combine2("", containers...);
}

int main() {
    myvec v1 = {"T", "C", "A"}, v2 = {"C", "G", "A"}, v3 = {"C", "G", "T"};

    combine(v1);
    combine(v1, v2);
    combine(v1, v2, v3);

    // Or even...
    std::vector v4 = {"T", "C", "A"};
    std::vector v5 = {'C', 'G', 'A'};
    std::vector v6 = {1 ,2 ,3};

    combine(v4);
    combine(v4, v5);
    combine(v4, v5, v6);

    return 0;
}