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copied!<p>What we are going to do, is split the players in 2 groups: contenders 1 & contenders 2. We're going to fill contenders a with consecutive players of the same school:</p> <p>If we name the schools a single letter for brevity, what we'll essentially have is:</p> <pre><code> A A A A B B B C C C D D E E F F </code></pre> <p>Or, if we flip it, it becomes clearer:</p> <pre><code> A C A C A D A D B E B E B F C F </code></pre> <p>What happens if one school has > the half of the total number of players? Well, let's see:</p> <pre><code> A A A A A A B B C D </code></pre> <p>So:</p> <pre><code> A A <= one A vs. A, which is unavoidable, but the method still works. A B A B A C A D </code></pre> <p>I cheated a bit here: I sorted out the players from the biggest school first. It however still works as long as we group schools together. Let's take my output of <code>$a = range('A','F'); shuffle($a):</code>, which here resulted in: FCADBE, which gives us:</p> <pre><code> F A F D C D C B C B A B A E A E </code></pre> <p>.. which works, also for A > half:</p> <pre><code> C A A A <= that one double again, unavoidable A D A B A B </code></pre> <p>Let's break this into parts. What we have to do is:</p> <ol> <li>sort the players by school</li> <li>break this sorted array into 2 groups.</li> <li>create pairs by adding on from the first group & one from the second group, in order.</li> </ol> <p>The advantage of cutting it down is so you can find answers:</p> <ol> <li><a href="https://stackoverflow.com/search?q=%5Bphp%5D+php+sort+multidimensional+array">hundreds of questions on SO</a></li> <li><a href="https://stackoverflow.com/questions/5393028/how-can-i-take-an-array-divide-it-by-two-and-create-two-lists">this is a nice answer</a></li> <li>We could use a <a href="http://www.php.net/manual/en/class.multipleiterator.php" rel="nofollow noreferrer">MultiIterator</a>, which would be a logical (and working) choice, but I'll show you another short way of creating pairs of 2 arrays (or triplets if you have 3 arrays, etc.)</li> </ol> <p>So, let's do that:</p> <pre><code> //sort by school $players = ... your array ... usort($players,function($playerA, $playerB){ return strcmp($playerA['school'], $playerB['school']); }); //voila, sorted //break this into 2 groups: $size = ceil(count($players) / 2); // round UP $groupA = array_slice($players,0,$size); $groupB = array_slice($players,$size); //create our duels array: $duels = array_map(null, $groupA, $groupB); </code></pre> <p><code>$duels</code> now has this content with your input:</p> <pre><code>[ [ { "name": "juan", "school": "ABC" }, { "name": "arnold", "school": "DEF" } ], [ { "name": "leo", "school": "ABC" }, { "name": "ash", "school": "ECD" } ], [ { "name": "simon", "school": "DEF" }, { "name": "luke", "school": "ECD" } ] ] </code></pre>

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