zip_iterator and sTL algorithms like random_shuffle

Andreas Fabri

30 Mar 2009 30 Mar '09

8:37 a.m.

Hello, I have two vectors and want to random_shuffle them the same way using the zip_iterator. I thought the code below would do it, but when I execute it I see that both sequences get screwded up. What do I wrong? Best regards, andreas #include <vector> #include #include <algorithm> #include <iostream> int main() { std::vector<int> I(8), J(8); for(int i = 0; i < I.size(); i++){ I[i] = J[i] = i; } std::random_shuffle(boost::make_zip_iterator(boost::make_tuple(I.begin(), J.begin())), boost::make_zip_iterator(boost::make_tuple(I.end(), J.end()))); for(int i = 0; i < I.size(); i++){ std::cout << I[i] << " " << J[i] << std::endl; } return 0; }

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Steven Watanabe

31 Mar 31 Mar

3:35 a.m.

New subject: zip_iterator and sTL algorithms like random_shuffle

AMDG Andreas Fabri wrote:

...

I have two vectors and want to random_shuffle them the same way using the zip_iterator. I thought the code below would do it, but when I execute it I see that both sequences get screwded up.

What do I wrong?

The problem is that std::iter_swap doesn't work for zip_iterator and there is no standard compliant way to fix it. In Christ, Steven Watanabe

Andreas Fabri

9:08 a.m.

New subject: zip_iterator and sTL algorithms like random_shuffle

Steven Watanabe wrote:

...

AMDG

Andreas Fabri wrote:

...
I have two vectors and want to random_shuffle them the same way using the zip_iterator. I thought the code below would do it, but when I execute it I see that both sequences get screwded up.

What do I wrong?

The problem is that std::iter_swap doesn't work for zip_iterator and there is no standard compliant way to fix it.

Hi Steven, And there is no means of making a partial specialization of iter_swap? And even if so, who guarantees that std::random_shuffle or std::sort use iter_swap to swap ? andreas

...

In Christ, Steven Watanabe

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Andreas Fabri

10:59 a.m.

New subject: zip_iterator and sTL algorithms like random_shuffle

Hi Steven, Adding a specialization for iter_swap typedef boost::tuple< std::vector<int>::iterator, std::vector<int>::iterator

...

iterator_tuple;

typedef boost::zip_iterator< iterator_tuple

...

ziterator;

namespace std { void iter_swap(ziterator a, ziterator b) { std::swap(a->get<0>(), b->get<0>()); std::swap(a->get<1>(), b->get<1>()); } } solved the problem for std::random_shuffle. For std::sort I provide a comparison functor for the tuple. but the compiler (VC8) complains about no match for _Rotate Any hint would be appreciated. andreas C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1719) : error C2665: 'std::_Rotate' : none of the 3 overloads could convert all the argument types C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1649): could be 'void std::_Rotate<_FwdIt>(_FwdIt,_FwdIt,_FwdIt,std::forward_iterator_tag)' with [ _FwdIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1666): or 'void std::_Rotate<_FwdIt>(_BidIt,_BidIt,_BidIt,std::bidirectional_iterator_tag)' with [ _FwdIt=boost::zip_iterator, _BidIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1709): or 'void std::_Rotate<_FwdIt>(_RanIt,_RanIt,_RanIt,std::random_access_iterator_tag)' with [ _FwdIt=boost::zip_iterator, _RanIt=boost::zip_iterator ] while trying to match the argument list '(boost::zip_iterator<IteratorTuple>, boost::zip_iterator<IteratorTuple>, boost::zip_iterator<IteratorTuple>, boost::detail::iterator_category_with_traversal)' with [ IteratorTuple=iterator_tuple ] and [ IteratorTuple=iterator_tuple ] and [ IteratorTuple=iterator_tuple ] and [ Category=std::input_iterator_tag, Traversal=boost::random_access_traversal_tag ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3125) : see reference to function template instantiation 'void std::rotate<_BidIt>(_FwdIt,_FwdIt,_FwdIt)' being compiled with [ _BidIt=boost::zip_iterator, _FwdIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3252) : see reference to function template instantiation 'void std::_Insertion_sort<_RanIt,_Pr>(_BidIt,_BidIt,_Pr)' being compiled with [ _RanIt=boost::zip_iterator, _Pr=Compare, _BidIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3261) : see reference to function template instantiation 'void std::_Sort<_RanIt,__int64,_Pr>(_RanIt,_RanIt,_Diff,_Pr)' being compiled with [ _RanIt=boost::zip_iterator, _Pr=Compare, _Diff=__int64 ] Steven Watanabe wrote:

...

AMDG

Andreas Fabri wrote:

...
I have two vectors and want to random_shuffle them the same way using the zip_iterator. I thought the code below would do it, but when I execute it I see that both sequences get screwded up.

What do I wrong?

The problem is that std::iter_swap doesn't work for zip_iterator and there is no standard compliant way to fix it.

In Christ, Steven Watanabe

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Ovanes Markarian

1:02 p.m.

New subject: zip_iterator and sTL algorithms like random_shuffle

This is not standard conform to introduce overloaded functions into std namespace. This posting might answer your question: http://groups.google.com/group/comp.lang.c++.moderated/browse_frm/thread/b39... It is pretty long, but worth reading it all. And that is what Steven means in his previous post, that there is no C++03 standard way to fix it. Greetings, Ovanes On Tue, Mar 31, 2009 at 12:59 PM, Andreas Fabri < andreas.fabri@geometryfactory.com> wrote:

...

Hi Steven,

Adding a specialization for iter_swap

typedef boost::tuple< std::vector<int>::iterator, std::vector<int>::iterator

...
iterator_tuple;

typedef boost::zip_iterator< iterator_tuple

...
ziterator;

namespace std {

void iter_swap(ziterator a, ziterator b) { std::swap(a->get<0>(), b->get<0>()); std::swap(a->get<1>(), b->get<1>()); }

}

solved the problem for std::random_shuffle.

For std::sort I provide a comparison functor for the tuple. but the compiler (VC8) complains about no match for _Rotate

Any hint would be appreciated.

andreas

C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1719) : error C2665: 'std::_Rotate' : none of the 3 overloads could convert all the argument types C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1649): could be 'void std::_Rotate<_FwdIt>(_FwdIt,_FwdIt,_FwdIt,std::forward_iterator_tag)' with [ _FwdIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1666): or 'void std::_Rotate<_FwdIt>(_BidIt,_BidIt,_BidIt,std::bidirectional_iterator_tag)' with [ _FwdIt=boost::zip_iterator, _BidIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(1709): or 'void std::_Rotate<_FwdIt>(_RanIt,_RanIt,_RanIt,std::random_access_iterator_tag)' with [ _FwdIt=boost::zip_iterator, _RanIt=boost::zip_iterator ] while trying to match the argument list '(boost::zip_iterator<IteratorTuple>, boost::zip_iterator<IteratorTuple>, boost::zip_iterator<IteratorTuple>, boost::detail::iterator_category_with_traversal)' with [ IteratorTuple=iterator_tuple ] and [ IteratorTuple=iterator_tuple ] and [ IteratorTuple=iterator_tuple ] and [ Category=std::input_iterator_tag, Traversal=boost::random_access_traversal_tag ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3125) : see reference to function template instantiation 'void std::rotate<_BidIt>(_FwdIt,_FwdIt,_FwdIt)' being compiled with [ _BidIt=boost::zip_iterator, _FwdIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3252) : see reference to function template instantiation 'void std::_Insertion_sort<_RanIt,_Pr>(_BidIt,_BidIt,_Pr)' being compiled with [ _RanIt=boost::zip_iterator, _Pr=Compare, _BidIt=boost::zip_iterator ] C:\Program Files (x86)\Microsoft Visual Studio 8\VC\INCLUDE\algorithm(3261) : see reference to function template instantiation 'void std::_Sort<_RanIt,__int64,_Pr>(_RanIt,_RanIt,_Diff,_Pr)' being compiled with [ _RanIt=boost::zip_iterator, _Pr=Compare, _Diff=__int64 ]

Steven Watanabe wrote:

...
AMDG

Andreas Fabri wrote:

...
I have two vectors and want to random_shuffle them the same way using the zip_iterator. I thought the code below would do it, but when I execute it I see that both sequences get screwded up.

What do I wrong?

The problem is that std::iter_swap doesn't work for zip_iterator and there is no standard compliant way to fix it.

In Christ, Steven Watanabe

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Steven Watanabe

6:57 p.m.

New subject: zip_iterator and sTL algorithms like random_shuffle

AMDG Ovanes Markarian wrote:

...

This is not standard conform to introduce overloaded functions into std namespace. This posting might answer your question: http://groups.google.com/group/comp.lang.c++.moderated/browse_frm/thread/b39...

It is pretty long, but worth reading it all. And that is what Steven means in his previous post, that there is no C++03 standard way to fix it.

Note that a trivial change will make this special case correct: inline void iter_swap<>(ziterator a, ziterator b) because specialization of std library templates is allowed. However, this doesn't work in general because function templates can't be partially specialized. In Christ, Steven Watanabe

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Andreas Fabri
Ovanes Markarian
Steven Watanabe