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- <title>Permutation Iterator</title>
- <meta name="author" content="Toon Knapen, David Abrahams, Roland Richter, Jeremy Siek" />
- <meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab" />
- <meta name="date" content="2006-09-11" />
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- <div class="document" id="permutation-iterator">
- <h1 class="title">Permutation Iterator</h1>
- <table class="docinfo" frame="void" rules="none">
- <col class="docinfo-name" />
- <col class="docinfo-content" />
- <tbody valign="top">
- <tr><th class="docinfo-name">Author:</th>
- <td>Toon Knapen, David Abrahams, Roland Richter, Jeremy Siek</td></tr>
- <tr><th class="docinfo-name">Contact:</th>
- <td><a class="first reference external" href="mailto:dave@boost-consulting.com">dave@boost-consulting.com</a>, <a class="last reference external" href="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</a></td></tr>
- <tr><th class="docinfo-name">Organization:</th>
- <td><a class="first reference external" href="http://www.boost-consulting.com">Boost Consulting</a>, Indiana University <a class="last reference external" href="http://www.osl.iu.edu">Open Systems
- Lab</a></td></tr>
- <tr><th class="docinfo-name">Date:</th>
- <td>2006-09-11</td></tr>
- <tr><th class="docinfo-name">Copyright:</th>
- <td>Copyright Toon Knapen, David Abrahams, Roland Richter, and Jeremy Siek 2003.</td></tr>
- </tbody>
- </table>
- <!-- Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">abstract:</th><td class="field-body"><!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- The permutation iterator adaptor provides a permuted view of a given
- range. That is, the view includes every element of the given range but
- in a potentially different order.</td>
- </tr>
- </tbody>
- </table>
- <div class="contents topic" id="table-of-contents">
- <p class="topic-title first">Table of Contents</p>
- <ul class="simple">
- <li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
- <li><a class="reference internal" href="#reference" id="id3">Reference</a><ul>
- <li><a class="reference internal" href="#permutation-iterator-requirements" id="id4"><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> requirements</a></li>
- <li><a class="reference internal" href="#permutation-iterator-models" id="id5"><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models</a></li>
- <li><a class="reference internal" href="#permutation-iterator-operations" id="id6"><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> operations</a></li>
- </ul>
- </li>
- <li><a class="reference internal" href="#example" id="id7">Example</a></li>
- </ul>
- </div>
- <div class="section" id="introduction">
- <h1><a class="toc-backref" href="#id2">Introduction</a></h1>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <p>The adaptor takes two arguments:</p>
- <blockquote>
- <ul class="simple">
- <li>an iterator to the range V on which the permutation
- will be applied</li>
- <li>the reindexing scheme that defines how the
- elements of V will be permuted.</li>
- </ul>
- </blockquote>
- <p>Note that the permutation iterator is not limited to strict
- permutations of the given range V. The distance between begin and end
- of the reindexing iterators is allowed to be smaller compared to the
- size of the range V, in which case the permutation iterator only
- provides a permutation of a subrange of V. The indexes neither need
- to be unique. In this same context, it must be noted that the past the
- end permutation iterator is completely defined by means of the
- past-the-end iterator to the indices.</p>
- </div>
- <div class="section" id="reference">
- <h1><a class="toc-backref" href="#id3">Reference</a></h1>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <pre class="literal-block">
- template< class ElementIterator
- , class IndexIterator
- , class ValueT = use_default
- , class CategoryT = use_default
- , class ReferenceT = use_default
- , class DifferenceT = use_default >
- class permutation_iterator
- {
- public:
- permutation_iterator();
- explicit permutation_iterator(ElementIterator x, IndexIterator y);
- template< class OEIter, class OIIter, class V, class C, class R, class D >
- permutation_iterator(
- permutation_iterator<OEIter, OIIter, V, C, R, D> const& r
- , typename enable_if_convertible<OEIter, ElementIterator>::type* = 0
- , typename enable_if_convertible<OIIter, IndexIterator>::type* = 0
- );
- reference operator*() const;
- permutation_iterator& operator++();
- ElementIterator const& base() const;
- private:
- ElementIterator m_elt; // exposition only
- IndexIterator m_order; // exposition only
- };
- template <class ElementIterator, class IndexIterator>
- permutation_iterator<ElementIterator, IndexIterator>
- make_permutation_iterator( ElementIterator e, IndexIterator i);
- </pre>
- <div class="section" id="permutation-iterator-requirements">
- <h2><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> requirements</a></h2>
- <p><tt class="docutils literal"><span class="pre">ElementIterator</span></tt> shall model Random Access Traversal Iterator.
- <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> shall model Readable Iterator. The value type of
- the <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> must be convertible to the difference type of
- <tt class="docutils literal"><span class="pre">ElementIterator</span></tt>.</p>
- </div>
- <div class="section" id="permutation-iterator-models">
- <h2><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models</a></h2>
- <p><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models the same iterator traversal concepts
- as <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> and the same iterator access concepts as
- <tt class="docutils literal"><span class="pre">ElementIterator</span></tt>.</p>
- <p>If <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> models Single Pass Iterator and
- <tt class="docutils literal"><span class="pre">ElementIterator</span></tt> models Readable Iterator then
- <tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models Input Iterator.</p>
- <p>If <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> models Forward Traversal Iterator and
- <tt class="docutils literal"><span class="pre">ElementIterator</span></tt> models Readable Lvalue Iterator then
- <tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models Forward Iterator.</p>
- <p>If <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> models Bidirectional Traversal Iterator and
- <tt class="docutils literal"><span class="pre">ElementIterator</span></tt> models Readable Lvalue Iterator then
- <tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models Bidirectional Iterator.</p>
- <p>If <tt class="docutils literal"><span class="pre">IndexIterator</span></tt> models Random Access Traversal Iterator and
- <tt class="docutils literal"><span class="pre">ElementIterator</span></tt> models Readable Lvalue Iterator then
- <tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models Random Access Iterator.</p>
- <p><tt class="docutils literal"><span class="pre">permutation_iterator<E1,</span> <span class="pre">X,</span> <span class="pre">V1,</span> <span class="pre">C2,</span> <span class="pre">R1,</span> <span class="pre">D1></span></tt> is interoperable
- with <tt class="docutils literal"><span class="pre">permutation_iterator<E2,</span> <span class="pre">Y,</span> <span class="pre">V2,</span> <span class="pre">C2,</span> <span class="pre">R2,</span> <span class="pre">D2></span></tt> if and only if
- <tt class="docutils literal"><span class="pre">X</span></tt> is interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt> and <tt class="docutils literal"><span class="pre">E1</span></tt> is convertible
- to <tt class="docutils literal"><span class="pre">E2</span></tt>.</p>
- </div>
- <div class="section" id="permutation-iterator-operations">
- <h2><a class="toc-backref" href="#id6"><tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> operations</a></h2>
- <p>In addition to those operations required by the concepts that
- <tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> models, <tt class="docutils literal"><span class="pre">permutation_iterator</span></tt> provides the
- following operations.</p>
- <p><tt class="docutils literal"><span class="pre">permutation_iterator();</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Default constructs <tt class="docutils literal"><span class="pre">m_elt</span></tt> and <tt class="docutils literal"><span class="pre">m_order</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">permutation_iterator(ElementIterator</span> <span class="pre">x,</span> <span class="pre">IndexIterator</span> <span class="pre">y);</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs <tt class="docutils literal"><span class="pre">m_elt</span></tt> from <tt class="docutils literal"><span class="pre">x</span></tt> and <tt class="docutils literal"><span class="pre">m_order</span></tt> from <tt class="docutils literal"><span class="pre">y</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <pre class="literal-block">
- template< class OEIter, class OIIter, class V, class C, class R, class D >
- permutation_iterator(
- permutation_iterator<OEIter, OIIter, V, C, R, D> const& r
- , typename enable_if_convertible<OEIter, ElementIterator>::type* = 0
- , typename enable_if_convertible<OIIter, IndexIterator>::type* = 0
- );
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs <tt class="docutils literal"><span class="pre">m_elt</span></tt> from <tt class="docutils literal"><span class="pre">r.m_elt</span></tt> and
- <tt class="docutils literal"><span class="pre">m_order</span></tt> from <tt class="docutils literal"><span class="pre">y.m_order</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*(m_elt</span> <span class="pre">+</span> <span class="pre">*m_order)</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">permutation_iterator&</span> <span class="pre">operator++();</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_order</span></tt></td>
- </tr>
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">ElementIterator</span> <span class="pre">const&</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_order</span></tt></td>
- </tr>
- </tbody>
- </table>
- <pre class="literal-block">
- template <class ElementIterator, class IndexIterator>
- permutation_iterator<ElementIterator, IndexIterator>
- make_permutation_iterator(ElementIterator e, IndexIterator i);
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">permutation_iterator<ElementIterator,</span> <span class="pre">IndexIterator>(e,</span> <span class="pre">i)</span></tt></td>
- </tr>
- </tbody>
- </table>
- </div>
- </div>
- <div class="section" id="example">
- <h1><a class="toc-backref" href="#id7">Example</a></h1>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <pre class="literal-block">
- using namespace boost;
- int i = 0;
- typedef std::vector< int > element_range_type;
- typedef std::list< int > index_type;
- static const int element_range_size = 10;
- static const int index_size = 4;
- element_range_type elements( element_range_size );
- for(element_range_type::iterator el_it = elements.begin() ; el_it != elements.end() ; ++el_it)
- *el_it = std::distance(elements.begin(), el_it);
- index_type indices( index_size );
- for(index_type::iterator i_it = indices.begin() ; i_it != indices.end() ; ++i_it )
- *i_it = element_range_size - index_size + std::distance(indices.begin(), i_it);
- std::reverse( indices.begin(), indices.end() );
- typedef permutation_iterator< element_range_type::iterator, index_type::iterator > permutation_type;
- permutation_type begin = make_permutation_iterator( elements.begin(), indices.begin() );
- permutation_type it = begin;
- permutation_type end = make_permutation_iterator( elements.begin(), indices.end() );
- std::cout << "The original range is : ";
- std::copy( elements.begin(), elements.end(), std::ostream_iterator< int >( std::cout, " " ) );
- std::cout << "\n";
- std::cout << "The reindexing scheme is : ";
- std::copy( indices.begin(), indices.end(), std::ostream_iterator< int >( std::cout, " " ) );
- std::cout << "\n";
- std::cout << "The permutated range is : ";
- std::copy( begin, end, std::ostream_iterator< int >( std::cout, " " ) );
- std::cout << "\n";
- std::cout << "Elements at even indices in the permutation : ";
- it = begin;
- for(i = 0; i < index_size / 2 ; ++i, it+=2 ) std::cout << *it << " ";
- std::cout << "\n";
- std::cout << "Permutation backwards : ";
- it = begin + (index_size);
- assert( it != begin );
- for( ; it-- != begin ; ) std::cout << *it << " ";
- std::cout << "\n";
- std::cout << "Iterate backward with stride 2 : ";
- it = begin + (index_size - 1);
- for(i = 0 ; i < index_size / 2 ; ++i, it-=2 ) std::cout << *it << " ";
- std::cout << "\n";
- </pre>
- <p>The output is:</p>
- <pre class="literal-block">
- The original range is : 0 1 2 3 4 5 6 7 8 9
- The reindexing scheme is : 9 8 7 6
- The permutated range is : 9 8 7 6
- Elements at even indices in the permutation : 9 7
- Permutation backwards : 6 7 8 9
- Iterate backward with stride 2 : 6 8
- </pre>
- <p>The source code for this example can be found <a class="reference external" href="../example/permutation_iter_example.cpp">here</a>.</p>
- </div>
- </div>
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