ceph/src/boost/libs/iterator/doc/permutation_iterator_eg.rst

   1 .. Copyright David Abrahams 2006. Distributed under the Boost
   2 .. Software License, Version 1.0. (See accompanying
   3 .. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   4
   5 ::
   6
   7     using namespace boost;
   8     int i = 0;
   9
  10     typedef std::vector< int > element_range_type;
  11     typedef std::list< int > index_type;
  12
  13     static const int element_range_size = 10;
  14     static const int index_size = 4;
  15
  16     element_range_type elements( element_range_size );
  17     for(element_range_type::iterator el_it = elements.begin() ; el_it != elements.end() ; ++el_it)
  18       *el_it = std::distance(elements.begin(), el_it);
  19
  20     index_type indices( index_size );
  21     for(index_type::iterator i_it = indices.begin() ; i_it != indices.end() ; ++i_it )
  22       *i_it = element_range_size - index_size + std::distance(indices.begin(), i_it);
  23     std::reverse( indices.begin(), indices.end() );
  24
  25     typedef permutation_iterator< element_range_type::iterator, index_type::iterator > permutation_type;
  26     permutation_type begin = make_permutation_iterator( elements.begin(), indices.begin() );
  27     permutation_type it = begin;
  28     permutation_type end = make_permutation_iterator( elements.begin(), indices.end() );
  29
  30     std::cout << "The original range is : ";
  31     std::copy( elements.begin(), elements.end(), std::ostream_iterator< int >( std::cout, " " ) );
  32     std::cout << "\n";
  33
  34     std::cout << "The reindexing scheme is : ";
  35     std::copy( indices.begin(), indices.end(), std::ostream_iterator< int >( std::cout, " " ) );
  36     std::cout << "\n";
  37
  38     std::cout << "The permutated range is : ";
  39     std::copy( begin, end, std::ostream_iterator< int >( std::cout, " " ) );
  40     std::cout << "\n";
  41
  42     std::cout << "Elements at even indices in the permutation : ";
  43     it = begin;
  44     for(i = 0; i < index_size / 2 ; ++i, it+=2 ) std::cout << *it << " ";
  45     std::cout << "\n";
  46
  47     std::cout << "Permutation backwards : ";
  48     it = begin + (index_size);
  49     assert( it != begin );
  50     for( ; it-- != begin ; ) std::cout << *it << " ";
  51     std::cout << "\n";
  52
  53     std::cout << "Iterate backward with stride 2 : ";
  54     it = begin + (index_size - 1);
  55     for(i = 0 ; i < index_size / 2 ; ++i, it-=2 ) std::cout << *it << " ";
  56     std::cout << "\n";
  57
  58
  59 The output is::
  60
  61     The original range is : 0 1 2 3 4 5 6 7 8 9
  62     The reindexing scheme is : 9 8 7 6
  63     The permutated range is : 9 8 7 6
  64     Elements at even indices in the permutation : 9 7
  65     Permutation backwards : 6 7 8 9
  66     Iterate backward with stride 2 : 6 8
  67
  68
  69 The source code for this example can be found `here`__.
  70
  71 __ ../example/permutation_iter_example.cpp