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<div class="title">ComparatorUtils<div class="ingroups"><a class="el" href="group__Kernel.html">Kernel</a></div></div> </div>
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<p>A collection of utilities for comparators.
<a href="#details">More...</a></p>
<p>A collection of utilities for comparators. </p>
<div class="fragment"><div class="line"><span class="preprocessor">#include <<a class="code" href="ComparatorUtils_8h.html">OpenMS/KERNEL/ComparatorUtils.h</a>></span></div>
</div><!-- fragment --><p>This file contains some lightweight class templates which simplify the (re-)usage and composition of <b>comparator classes</b>:</p>
<ul>
<li>ReverseComparator (reverse the direction of comparison)</li>
<li>LexicographicComparator (combine comparators lexicographically)</li>
<li>PointerComparator (compare pointers like the type they point to)</li>
</ul>
<p>We provide corresponding "make-functions" so that you will not need to write out the type names in the template instantiation.</p>
<p>We explain this with a simple example. First a few prerequisites.</p>
<div class="fragment"><div class="line"><span class="comment">// --------------------------------------------------------------------------</span></div>
<div class="line"><span class="comment">// OpenMS -- Open-Source Mass Spectrometry</span></div>
<div class="line"><span class="comment">// --------------------------------------------------------------------------</span></div>
<div class="line"><span class="comment">// Copyright The OpenMS Team -- Eberhard Karls University Tuebingen,</span></div>
<div class="line"><span class="comment">// ETH Zurich, and Freie Universitaet Berlin 2002-2013.</span></div>
<div class="line"><span class="comment">//</span></div>
<div class="line"><span class="comment">// This software is released under a three-clause BSD license:</span></div>
<div class="line"><span class="comment">// * Redistributions of source code must retain the above copyright</span></div>
<div class="line"><span class="comment">// notice, this list of conditions and the following disclaimer.</span></div>
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<div class="line"><span class="comment">// without specific prior written permission.</span></div>
<div class="line"><span class="comment">// For a full list of authors, refer to the file AUTHORS.</span></div>
<div class="line"><span class="comment">// --------------------------------------------------------------------------</span></div>
<div class="line"><span class="comment">// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"</span></div>
<div class="line"><span class="comment">// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE</span></div>
<div class="line"><span class="comment">// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE</span></div>
<div class="line"><span class="comment">// ARE DISCLAIMED. IN NO EVENT SHALL ANY OF THE AUTHORS OR THE CONTRIBUTING</span></div>
<div class="line"><span class="comment">// INSTITUTIONS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,</span></div>
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<div class="line"><span class="comment">// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.</span></div>
<div class="line"><span class="comment">//</span></div>
<div class="line"></div>
<div class="line"><span class="preprocessor">#include <<a class="code" href="ComparatorUtils_8h.html">OpenMS/KERNEL/ComparatorUtils.h</a>></span></div>
<div class="line"><span class="preprocessor">#include <<a class="code" href="StandardTypes_8h.html">OpenMS/KERNEL/StandardTypes.h</a>></span></div>
<div class="line"><span class="keyword">using</span> <a class="code" href="group__Concept.html#ga7cc214a236ad3bb6ad435bdcf5262a3f">OpenMS::Int</a>;</div>
<div class="line"><span class="keyword">using</span> <a class="code" href="group__Concept.html#gaba0996d26f7be2572973245b51852757">OpenMS::UInt</a>;</div>
<div class="line"><span class="keyword">using</span> <a class="code" href="group__Concept.html#gaf9ecec2d692138fab9167164a457cbd4">OpenMS::Size</a>;</div>
<div class="line"><span class="keyword">using</span> <a class="code" href="group__Concept.html#gab685845059e8a2c92743427d9a698c70">OpenMS::Real</a>;</div>
<div class="line"><span class="keyword">using</span> <a class="code" href="classOpenMS_1_1String.html">OpenMS::String</a>;</div>
</div><!-- fragment --></p>
<p>The class IntRealString has three data members. The class IntRealStringVector is a vector of IntRealString. We add some print() methods for convenience. <div class="fragment"><div class="line"></div>
<div class="line"><span class="comment">// Simple class with three data members</span></div>
<div class="line"><span class="keyword">class </span>IntRealString</div>
<div class="line">{</div>
<div class="line"><span class="keyword">public</span>:</div>
<div class="line"> IntRealString(<a class="code" href="classInt.html">Int</a> i, <a class="code" href="classReal.html">Real</a> r, String s) :</div>
<div class="line"> i_(i), r_(r), s_(s) {}</div>
<div class="line"> IntRealString(<span class="keyword">const</span> IntRealString & rhs) :</div>
<div class="line"> i_(rhs.i_), r_(rhs.r_), s_(rhs.s_) {}</div>
<div class="line"></div>
<div class="line"> <span class="keywordtype">void</span> print()<span class="keyword"> const</span></div>
<div class="line"><span class="keyword"> </span>{</div>
<div class="line"> std::cout << <span class="stringliteral">"("</span> << i_ << <span class="stringliteral">", "</span> << r_ << <span class="stringliteral">", "</span> << s_ << <span class="stringliteral">")"</span> << std::endl;</div>
<div class="line"> }</div>
<div class="line"></div>
<div class="line"> <a class="code" href="classInt.html">Int</a> i_;</div>
<div class="line"> <a class="code" href="classReal.html">Real</a> r_;</div>
<div class="line"> String s_;</div>
<div class="line">};</div>
<div class="line"></div>
<div class="line"><span class="comment">// A vector of IntRealString objects</span></div>
<div class="line"><span class="keyword">class </span>IntRealStringVector :</div>
<div class="line"> <span class="keyword">public</span> std::vector<IntRealString></div>
<div class="line">{</div>
<div class="line"><span class="keyword">public</span>:</div>
<div class="line"> <span class="keywordtype">void</span> print()<span class="keyword"> const</span></div>
<div class="line"><span class="keyword"> </span>{</div>
<div class="line"> <span class="keywordflow">for</span> (Size i = 0; i < size(); ++i) (*<span class="keyword">this</span>)[i].print();</div>
<div class="line"> std::cout << std::endl;</div>
<div class="line"> }</div>
<div class="line"></div>
<div class="line">};</div>
</div><!-- fragment --></p>
<p>Now we will exercise various ways of sorting such a vector.</p>
<p>Of course, we could use the std::sort algorithm with a comparison function like the following. <div class="fragment"><div class="line"></div>
<div class="line"><span class="comment">// Comparison function</span></div>
<div class="line"><span class="keywordtype">bool</span> lessByInt(IntRealString left, IntRealString right)</div>
<div class="line">{</div>
<div class="line"> <span class="keywordflow">return</span> left.i_ < right.i_;</div>
<div class="line">}</div>
</div><!-- fragment --></p>
<p>This is straightforward but does not generalize well. Instead we introduce three <b>comparator classes</b>: <div class="fragment"><div class="line"></div>
<div class="line"><span class="comment">// Comparator class</span></div>
<div class="line"><span class="keyword">struct </span>LessByInt :</div>
<div class="line"> std::binary_function<IntRealString, IntRealString, bool></div>
<div class="line">{</div>
<div class="line"> <span class="keywordtype">bool</span> operator()(IntRealString left, IntRealString right)<span class="keyword"> const </span>{ <span class="keywordflow">return</span> left.i_ < right.i_; }</div>
<div class="line">};</div>
<div class="line"></div>
<div class="line"><span class="comment">// Comparator class</span></div>
<div class="line"><span class="keyword">struct </span>LessByReal :</div>
<div class="line"> std::binary_function<IntRealString, IntRealString, bool></div>
<div class="line">{</div>
<div class="line"> <span class="keywordtype">bool</span> operator()(IntRealString left, IntRealString right)<span class="keyword"> const </span>{ <span class="keywordflow">return</span> left.r_ < right.r_; }</div>
<div class="line">};</div>
<div class="line"></div>
<div class="line"><span class="comment">// Comparator class</span></div>
<div class="line"><span class="keyword">struct </span>LessByString :</div>
<div class="line"> std::binary_function<IntRealString, IntRealString, bool></div>
<div class="line">{</div>
<div class="line"> <span class="keywordtype">bool</span> operator()(IntRealString left, IntRealString right)<span class="keyword"> const </span>{ <span class="keywordflow">return</span> left.s_ < right.s_; }</div>
<div class="line">};</div>
</div><!-- fragment --> Note how the std::binary_function template provides the necessary type information (sometimes this is called "reflection").</p>
<p>Now we show various uses of the reverseComparator and lexicographicComparator function templates. <div class="fragment"><div class="line"></div>
<div class="line"><a class="code" href="classInt.html">Int</a> <a class="code" href="RNPxl_8C.html#a217dbf8b442f20279ea00b898af96f52">main</a>()</div>
<div class="line">{</div>
<div class="line"> IntRealStringVector vec;</div>
<div class="line"> vec.push_back(IntRealString(1, 4.5f, <span class="stringliteral">"paul"</span>));</div>
<div class="line"> vec.push_back(IntRealString(2, 4.5f, <span class="stringliteral">"josie"</span>));</div>
<div class="line"> vec.push_back(IntRealString(1, 4.5f, <span class="stringliteral">"john"</span>));</div>
<div class="line"> vec.push_back(IntRealString(2, 3.9f, <span class="stringliteral">"kim"</span>));</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"After initialization:"</span> << std::endl;</div>
<div class="line"> vec.print();</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"Sorted using lessByInt function:"</span> << std::endl;</div>
<div class="line"> std::sort(vec.begin(), vec.end(), lessByInt);</div>
<div class="line"> vec.print();</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"Sorted using LessByInt comparator class:"</span> << std::endl;</div>
<div class="line"> std::sort(vec.begin(), vec.end(), LessByInt());</div>
<div class="line"> vec.print();</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"Sorted using reversed LessByInt comparator class:"</span> << std::endl;</div>
<div class="line"> std::sort(vec.begin(), vec.end(), <a class="code" href="namespaceOpenMS.html#a74e80d32be63268d8a46039297e18cc6">OpenMS::reverseComparator</a>(LessByInt()));</div>
<div class="line"> vec.print();</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"Sorted using lexicographic order: 1. LessByInt, 2. LessByReal"</span> << std::endl;</div>
<div class="line"> std::sort(vec.begin(), vec.end(), <a class="code" href="namespaceOpenMS.html#ac4e734db514973176bfe65e0fa9905ae">OpenMS::lexicographicComparator</a>(LessByInt(), LessByReal()));</div>
<div class="line"> vec.print();</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"Sorted using lexicographic order: 1. reversed LessByInt, 2. LessByReal, 3. LessByString"</span> << std::endl;</div>
<div class="line"> std::sort(vec.begin(), vec.end(),</div>
<div class="line"> <a class="code" href="namespaceOpenMS.html#ac4e734db514973176bfe65e0fa9905ae">OpenMS::lexicographicComparator</a></div>
<div class="line"> (<a class="code" href="namespaceOpenMS.html#ac4e734db514973176bfe65e0fa9905ae">OpenMS::lexicographicComparator</a></div>
<div class="line"> (</div>
<div class="line"> <a class="code" href="namespaceOpenMS.html#a74e80d32be63268d8a46039297e18cc6">OpenMS::reverseComparator</a>(LessByInt()),</div>
<div class="line"> LessByReal()</div>
<div class="line"> ),</div>
<div class="line"> LessByString()</div>
<div class="line"> )</div>
<div class="line"> );</div>
<div class="line"> vec.print();</div>
</div><!-- fragment --></p>
<p>And here is an application of the pointerComparator function template: <div class="fragment"><div class="line"></div>
<div class="line"> <span class="comment">// vector of pointers into vec</span></div>
<div class="line"> std::vector<const IntRealString *> ptr_vec;</div>
<div class="line"> <span class="keywordflow">for</span> (Size i = 0; i < vec.size(); ++i)</div>
<div class="line"> {</div>
<div class="line"> ptr_vec.push_back(&vec[i]);</div>
<div class="line"> }</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"ptr_vec before sorting"</span> << std::endl;</div>
<div class="line"> <span class="keywordflow">for</span> (Size i = 0; i < ptr_vec.size(); ++i)</div>
<div class="line"> ptr_vec[i]->print();</div>
<div class="line"> std::cout << std::endl;</div>
<div class="line"></div>
<div class="line"> std::sort(ptr_vec.begin(), ptr_vec.end(), <a class="code" href="namespaceOpenMS.html#aeb071107569224c672893cd945dff7fe">OpenMS::pointerComparator</a>(LessByString()));</div>
<div class="line"></div>
<div class="line"> std::cout << <span class="stringliteral">"ptr_vec after sorting with pointerComparator(LessByString())"</span> << std::endl;</div>
<div class="line"> <span class="keywordflow">for</span> (Size i = 0; i < ptr_vec.size(); ++i)</div>
<div class="line"> ptr_vec[i]->print();</div>
<div class="line"> std::cout << std::endl;</div>
<div class="line"></div>
<div class="line"> <span class="keywordflow">return</span> 0;</div>
<div class="line">} <span class="comment">//end of main</span></div>
</div><!-- fragment --></p>
<p>The output of the example program is: </p>
<div class="fragment"><div class="line">After initialization:</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"></div>
<div class="line">Sorted <span class="keyword">using</span> lessByInt <span class="keyword">function</span>:</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"></div>
<div class="line">Sorted <span class="keyword">using</span> LessByInt comparator <span class="keyword">class</span>:</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"></div>
<div class="line">Sorted <span class="keyword">using</span> reversed LessByInt comparator <span class="keyword">class</span>:</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"></div>
<div class="line">Sorted <span class="keyword">using</span> lexicographic order: 1. LessByInt, 2. LessByReal</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"></div>
<div class="line">Sorted <span class="keyword">using</span> lexicographic order: 1. reversed LessByInt, 2. LessByReal, 3. LessByString</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"></div>
<div class="line">ptr_vec before sorting</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (1, 4.5, paul)</div>
<div class="line"></div>
<div class="line">ptr_vec after sorting with <a class="code" href="structOpenMS_1_1PointerComparator.html#aeb071107569224c672893cd945dff7fe">pointerComparator</a>(LessByString())</div>
<div class="line"> (1, 4.5, john)</div>
<div class="line"> (2, 4.5, josie)</div>
<div class="line"> (2, 3.9, kim)</div>
<div class="line"> (1, 4.5, paul)</div>
</div><!-- fragment --><p>Note that pointerComparator can also be used with full-blown iterator classes. (It should work with everything that provides an <a class="el" href="namespaceOpenMS.html#a938a33df5856a90299d3d7fbf9a4c02c" title="Scalar multiplication (a bit inefficient) ">operator*()</a>, but the typedefs will always be pointers.)</p>
<p>Note that these templates can also be used with different types for "left" and "right". </p>
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