What I want to do: I want to sort 2, or 3, or N vectors, locked together, without copying them into a tuple. That is, leaving verbosity aside, something like:
vector<int> v1 = { 1, 2, 3, 4, 5};
vector<double> v2 = { 11, 22, 33, 44, 55};
vector<long> v3 = {111, 222, 333, 444, 555};
typedef tuple<int&,double&,long&> tup_t;
sort(zip(v1,v2,v3),[](tup_t t1, tup_t t2){ return t1.get<0>() > t2.get<0>(); });
for(auto& t : zip(v1,v2,v3))
cout << t.get<0>() << " " << t.get<1>() << " " << t.get<2>() << endl;
This should output:
5 55 555
4 44 444
...
1 11 111
How I am doing it right now: I have implemented my own quicksort, where the first array I pass is used for the comparison, and the permutations are applied to all other arrays. I just couldn't figure out how to reuse std::sort for my problem (e.g. extract permutations).
What I've tryed: boost::zip_iterator and boost::zip_range (with boost::combine range), but both std::sort and boost::range::algorithm::sort complain that the iterators/ranges are read only and not random access...
Question: How do I sort N vectors in lock step (zipped)? The problem looks pretty generic and common so I guess there must be an easy solution through a probably very complex library but I just can't find it...
Remarks: yes, there are similar questions in stackoverflow, this question gets asked a lot in different forms. However they are always closed with one of the following answers:
Hints:
[...] the fundamental problem is that "pairs" of array references do not behave like they should [...] I simply decided to abuse the notation of an iterator and write something that works. This involved writing, effectively, a non-conforming iterator where the reference of the value type is not the same as the reference type.
Answer: see comment by interjay below (this also partially answers the future question):
#include "tupleit.hh"
#include <vector>
#include <iostream>
#include <boost/range.hpp>
#include <boost/range/algorithm/sort.hpp>
#include <boost/range/algorithm/for_each.hpp>
template <typename... T>
auto zip(T&... 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() {
typedef boost::tuple<int&,double&,long&> tup_t;
std::vector<int> a = { 1, 2, 3, 4 };
std::vector<double> b = { 11, 22, 33, 44 };
std::vector<long> c = { 111, 222, 333, 444 };
auto print = [](tup_t t){ std::cout << t.get<0>() << " " << t.get<1>() << " " << t.get<2>() << std::endl; };
boost::for_each( zip(a, b, c), print);
boost::sort( zip(a, b, c), [](tup_t i, tup_t j){ return i.get<0>() > j.get<0>(); });
for ( auto tup : zip(a, b, c) ) print(tup);
return 0;
}
Future question: the previous answer works for sequence containers. Could we get it also to work on sortable containers (e.g. sequences and lists)? This would require random_access and bidirectional TupleIterators as well as a sort algorithm that works on bidirectional iterators.
Update: this works for combinations of sequence-like containers. However mixing a list would require that std::sort supported BidirectionalIterators (which does not).
Here's a working example based on the range-v3 Library that has been proposed for Standardization
#include <range/v3/all.hpp>
#include <iostream>
using namespace ranges;
int main()
{
std::vector<int> a1{15, 7, 3, 5};
std::vector<int> a2{ 1, 2, 6, 21};
sort(view::zip(a1, a2), std::less<>{}, &std::pair<int, int>::first);
std::cout << view::all(a1) << '\n';
std::cout << view::all(a2) << '\n';
}
Live Example (requires recent compiler with good C++14 support, not VS 2015).