How to Sort Zipped Containers in C Using Boost or Range-v3?

Sorting Zipped Containers in C Using Boost or the STL

Sorting multiple containers simultaneously while maintaining their synchronized order is a common challenge. This question explores solutions using the Boost library and the STL, addressing the limitations of copying data into tuples or structures.

The fundamental issue lies in the behavior of "pairs" of array references, which do not adhere to the expected iterator characteristics. This has prompted the development of non-conforming iterators that effectively dissociate the value type reference from the reference type.

Boost Solution

The accepted answer from interjay leverages the "tupleit.hh" library, which provides custom tuple iterators that enable sorting of zipped containers.

#include "tupleit.hh"
#include <vector>
#include <iostream>
#include <boost/range.hpp>
#include <boost/range/algorithm/sort.hpp>

// Custom zip function
template <typename... T>
auto zip(T&amp;... containers)
    -> boost::iterator_range<decltype(iterators::makeTupleIterator(std::begin(containers)...))> {
  return boost::make_iterator_range(iterators::makeTupleIterator(std::begin(containers)...),
                                      iterators::makeTupleIterator(std::end(containers)...));
}

int main() {
  // Example data
  std::vector<int> a = {1, 2, 3, 4};
  std::vector<double> b = {11, 22, 33, 44};
  std::vector<long> c = {111, 222, 333, 444};

  // Sort zipped containers
  boost::sort(zip(a, b, c), [](auto& i, auto& j) { return i.get<0>() > j.get<0>(); });

  // Print sorted results
  for (auto& tup : zip(a, b, c)) {
    std::cout << tup.get<0>() << " " << tup.get<1>() << " " << tup.get<2>() << std::endl;
  }

  return 0;
}

This solution allows sorting of sequence containers without copying them into separate structures.

Range-v3 Solution

An alternative approach utilizing the range-v3 library, which proposes extensions to the STL, offers an elegant and concise solution.

#include <range/v3/all.hpp>
#include <iostream>

using namespace ranges;

int main() {
  // Example data
  std::vector<int> a1{15, 7, 3, 5};
  std::vector<int> a2{1, 2, 6, 21};

  // Sort zipped containers
  sort(view::zip(a1, a2), std::less<>{}, &amp;std::pair<int, int>::first);

  // Print sorted results
  for (auto& [x, y] : view::zip(a1, a2)) {
    std::cout << x << " " << y << std::endl;
  }
}

Considerations for Mixed Containers

While the presented solutions address the sorting of sequence-like containers, extending them to support mixed types (e.g., lists and sequences) would require the development of specialized BidirectionalIterators and the implementation of a sort algorithm compatible with such iterators. However, it is worth noting that the STL's std::sort does not support BidirectionalIterators.

In conclusion, both the Boost and range-v3 solutions provide efficient and customizable means of sorting multiple containers in lock step, opening up new possibilities for data manipulation in C .

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