How to link elements from different vectors with each other? - c++

Question

I want to write a program which reads names in a vector. After that it should read ages into another vector. (that's done)
The first element of the name-vector should be connected to the first element of the age-vector, so if I use any kind of sort() function on the name-vector the age-vector gets sorted as well.
Is there any way to realize this in an easy way?
class Name_pairs {
public:
//member functions
int read_names();
int read_ages();
int print();
private:
vector<double> age;
vector<string> name;
};
int Name_pairs::read_names() {
cout << "Please enter different names, you want to store in a vector:\n";
for (string names; cin >> names;) {
name.push_back(names);
}
cin.clear();
cout << "You entered following names:\n\t";
for (int i = 0; i < name.size(); i++) {
cout << name[i] << " \n\t";
}
return 0;
}
int Name_pairs::read_ages() {
cout << "\nPlease enter an age for every name in the vector.\n";
for (double ages; cin >> ages;) {
age.push_back(ages);
}
return 0;
}

Answer 1

I think you need a std::vector of a coupled type.
struct Name_pair {
double age;
string name;
};
Than you can use std::vector<Name_pair> and use a lambda
auto comparator = [](const Name_pair& first, const Name_pair& second){return first.age <second.age;};
to sort your vector with std::sort.
Name_pairs = std::vector<Name_pair>;
// fill vector
std::sort(Name_pairs.begin(), Name_pairs.end(), comparator);
Here is a working example.
#include <vector>
#include <algorithm>
#include <string>
#include <iostream>
struct Name_pair {
double age;
std::string name;
};
int main() {
std::vector<Name_pair> Name_pairs{{13, "Hallo"}, {32, "Welt"}, {1, "Georg"}};
auto comparator = [](const Name_pair& first, const Name_pair& second) { return first.age < second.age; };
std::sort(Name_pairs.begin(), Name_pairs.end(), comparator);
for (const auto np : Name_pairs) {
std::cout << np.name << "\n";
}
}
It prints
Georg
Hallo
Welt

Answer 2

If you want to implement a data-oriented design by using separate vectors instead of a single vector of classes, you could use a vector of indeces and sort it.
The following is just an example:
#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
class Customers
{
std::vector<double> ages_;
std::vector<std::string> names_;
template <typename Comparator>
auto make_indeces(Comparator &&comp)
{
std::vector<size_t> indeces(names_.size());
std::iota(indeces.begin(), indeces.end(), 0);
std::sort(indeces.begin(), indeces.end(), comp);
return indeces;
}
template <typename Type>
void reorder_vector(std::vector<Type> &src, std::vector<size_t> const &indeces)
{
std::vector<Type> tmp;
tmp.reserve(src.size());
std::generate_n(
std::back_inserter(tmp), src.size(),
[&src, idx = indeces.cbegin()] () mutable {
return src[*(idx++)];
});
src = std::move(tmp);
}
public:
void add(std::string const &name, double age)
{
names_.push_back(name);
ages_.push_back(age);
}
void sort_by_names()
{
auto indeces = make_indeces([this] (size_t i, size_t j) {
return names_[i] < names_[j];
});
reorder_vector(names_, indeces);
reorder_vector(ages_, indeces);
}
void show_sorted_by_ages()
{
auto indeces = make_indeces([this] (size_t i, size_t j) {
return ages_[i] < ages_[j];
});
for (auto i : indeces)
std::cout << names_[i] << ' ' << ages_[i] << '\n';
}
void show()
{
for (size_t i = 0; i < names_.size(); ++i)
std::cout << names_[i] << ' ' << ages_[i] << '\n';
}
};
int main(void)
{
Customers c;
c.add("Adam", 23);
c.add("Eve", 21);
c.add("Snake", 66.6);
c.add("Apple", 3.14);
std::cout << "Sorted by ages (doesn't modify the internal order):\n";
c.show_sorted_by_ages();
std::cout << "\nInternal order:\n";
c.show();
c.sort_by_names();
std::cout << "\nInternal order after sorting by names:\n";
c.show();
}
Testable HERE.