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POPHP Random numbers with weights on two levels
 

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  1. POPHP Random numbers with weights on two levels
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    <p>I have growing number of so called Battles grouped in different Ranks. I want to randomize the battles shown to the user. The show rate to be defined by the Rank at first place (higher rank - more impressions) and the second level is to get a random battle from the collection in this rank. Every battle in the rank has it's own number of impressions.</p> <p>In $battles I get the battles from the DB and i perform some calculations to define the show rate and the impressions that each rank should get.</p> <pre><code>foreach ($battles as $el =&gt; &amp;$values) { $values['show_rate'] = $values['rank'] * 100 / $totals['sum_of_ranks']; $values['dedicated_impressions'] = $totals['total_battle_impressions'] * $values['show_rate'] / 100; $values['impressions_left'] = $values['dedicated_impressions'] - $values['sum_of_impressions']; } </code></pre> <p>This is the result of the previous cycle. In the key <code>battle_ids</code> i have the ids of the battles in this rank, in <code>battle_impressions</code> i have the impressions of the same battles ordered in the same way.</p> <pre><code> $battles = array( 0 =&gt; array( 'battles_in_rank' =&gt; '1', 'battle_ids' =&gt; array( 0 =&gt; '28', ), 'battle_impressions' =&gt; array( 0 =&gt; '3', ), 'sum_of_impressions' =&gt; '3', 'rank' =&gt; '0', 'show_rate' =&gt; 0, 'dedicated_impressions' =&gt; 0, 'impressions_left' =&gt; -3, ), 1 =&gt; array( 'battles_in_rank' =&gt; '4', 'battle_ids' =&gt; array( 0 =&gt; '27', 1 =&gt; '19', 2 =&gt; '18', 3 =&gt; '17', ), 'battle_impressions' =&gt; array( 0 =&gt; '0', 1 =&gt; '0', 2 =&gt; '0', 3 =&gt; '0', ), 'sum_of_impressions' =&gt; '0', 'rank' =&gt; '1', 'show_rate' =&gt; 6.6666666666667, 'dedicated_impressions' =&gt; 230.53333333333, 'impressions_left' =&gt; 230.53333333333, ), 2 =&gt; array( 'battles_in_rank' =&gt; '2', 'battle_ids' =&gt; array( 0 =&gt; '7', 1 =&gt; '3', ), 'battle_impressions' =&gt; array( 0 =&gt; '0', 1 =&gt; '3', ), 'sum_of_impressions' =&gt; '3', 'rank' =&gt; '3', 'show_rate' =&gt; 20, 'dedicated_impressions' =&gt; 691.6, 'impressions_left' =&gt; 688.6, ), 3 =&gt; array( 'battles_in_rank' =&gt; '2', 'battle_ids' =&gt; array( 0 =&gt; '12', 1 =&gt; '5', ), 'battle_impressions' =&gt; array( 0 =&gt; '17', 1 =&gt; '1', ), 'sum_of_impressions' =&gt; '18', 'rank' =&gt; '4', 'show_rate' =&gt; 26.666666666667, 'dedicated_impressions' =&gt; 922.13333333333, 'impressions_left' =&gt; 904.13333333333, ), 4 =&gt; array( 'battles_in_rank' =&gt; '1', 'battle_ids' =&gt; array( 0 =&gt; '2', ), 'battle_impressions' =&gt; array( 0 =&gt; '3434', ), 'sum_of_impressions' =&gt; '3434', 'rank' =&gt; '7', 'show_rate' =&gt; 46.666666666667, 'dedicated_impressions' =&gt; 1613.7333333333, 'impressions_left' =&gt; -1820.2666666667, ), ); </code></pre> <p>After i get all this information i perform a clean up to get nice result for random function.</p> <pre><code>$elements = array(); $weights = array(); foreach ($battles as $el =&gt; &amp;$values) { $elements[] = array($values['battle_ids'], $values['battle_impressions']); $weights[] = $values['show_rate']; } </code></pre> <p>Here is the random function that i have at the moment:</p> <pre><code>public function getRandom($values, $weights) { $pos = mt_rand(1, array_sum($weights)); $em = 0; foreach ($values as $k =&gt; $v) { $em += $weights[$k]; if ($em &gt;= $pos) { if (is_array($v)) { return $this-&gt;getRandom($v[0], $v[1]); } else { return $v; } } } } </code></pre> <p>And i call it like that to get one random battle id.</p> <pre><code>$this-&gt;getRandom($elements, $weights); </code></pre> <p>What i need is having 5 or 10 unique random IDs.</p> <p>It works but this function gives me only one random element of each call, and when i call it several times i get the same id very often, like 6 out of 10 times.</p> <p>For example if i need 5 random battles i have to call the function in a cycle with 20-30 iterations to get 5 unique random battles. If the battles in the higher ranks are over it should fill the array with battles in lower ranks, so i always end up with 5 battles (or 10). </p> <p>The second level of randomization should be the battles in one rank, weighted by their impressions. That's why the random function is recursive.</p>
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