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POboost::multi_index_container with random_access and ordered_unique
 

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    <p>I have a problem getting <code>boost::multi_index_container</code> work with random-access and with orderd_unique at the same time. (I'm sorry for the lengthly question, but I think I should use an example..)</p> <p>Here an example: Suppose I want to produce N objects in a factory and for each object I have a demand to fulfill (this demand is known at creation of the multi-index). Well, within my algorithm I get intermediate results, which I store in the following class:</p> <pre><code>class intermediate_result { private: std::vector&lt;int&gt; parts; // which parts are produced int used_time; // how long did it take to produce ValueType max_value; // how much is it worth }; </code></pre> <p>The vector <code>parts</code> descibes, which objects are produced (its length is N and it is lexicographically smaller then my coresp demand-vector!) - for each such vector I know the used_time as well. Additionally I get a value for this vector of produced objects.</p> <p>I got another constraint so that I can't produce every object - my algorithm needs to store several <code>intermediate_result</code>-objects in a data-structure. And here <code>boost::multi_index_container</code> is used, because the pair of <code>parts</code> and <code>used_time</code> describes a unique <code>intermediate_result</code> (and it should be unique in my data-structure) but the <code>max_value</code> is another index I'll have to consider, because my algorithm always needs the <code>intermediate_result</code> with the highest <code>max_value</code>.</p> <p>So I tried to use <code>boost::multi_index_container</code> with <code>ordered_unique&lt;&gt;</code> for my "parts&amp;used_time-pair" and <code>ordered_non_unique&lt;&gt;</code> for my <code>max_value</code> (different <code>intermediate_result</code>-objects may have the same value).</p> <p>The problem is: the predicate, which is needed to decide which "parts&amp;used_time-pair" is smaller, uses <code>std::lexicographical_compare</code> on my <code>parts</code>-vector and hence is very slow for many <code>intermediate_result</code>-objects. But there would be a solution: my demand for each object isn't that high, therefore I could store on each <strong>possible</strong> parts-vector the intermediate results uniquely by its <code>used_time</code>.</p> <p>For example: if I have a demand-vector <code>( 2 , 3 , 1)</code> then I need a data-structure which stores <code>(2+1)*(3+1)*(1+1)=24</code> possible parts-vectors and on each such entry the different used_times, which have to be unique! (storing the smallest time is insufficient - for example: if my additional constraint is: to meet a given time exactly for production)</p> <p>But how do I combine a <code>random_access&lt;&gt;</code>-index with an <code>ordered_unique&lt;&gt;</code>-index?<br> (<a href="http://www.boost.org/doc/libs/1_40_0/libs/multi_index/doc/examples.html#example11" rel="nofollow noreferrer">Example11</a> didn't help me on this one..)</p>
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    1. COohh, I forgot to mention: The predicate for the uniqueness of the "parts&used_time-pair" is not faster if I test the used_time before the vector. Additionally I tried to use `hashed_unique<>` instead of `ordered_unique<>` - but I had to push the vector and the used_time in a string to be able to use the hash (the resulting multi_index was slower). Is there a better way to use the hash or use an own random_access data-structure (which guarantees uniqueness) linked with the other ordering index (for max_value)?
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