Online PHP editor | refs for cRU6e

<?php $articles = [ [ "id" => 0, "title" => "lorem", "reference" => "A" ], [ "id" => 1, "title" => "ipsum", "reference" => "B" ], [ "id" => 2, "title" => "dolor", "reference" => "C" ], [ "id" => 3, "title" => "sit", "reference" => "A" ] ]; $found = []; foreach ($articles as $index => ['reference' => $ref]) { if (!isset($found[$ref])) { $found[$ref] = $index; } else { unset($articles[$index], $articles[$found[$ref]]); } } var_export($articles);