Online PHP editor | output for msUPQ

<?php declare(strict_types=1); $data = [ '-MC1kTfrrDHY3ZbidJ4Q' => [ 'from' => 'lSUfZ4sgEJd', 'message' => 'test message four no more!', 'startedAt' => '2020-07-12 11:21:10', 'to' => 'CWgPqdn3YweN', ], '-MC09BsjtXP0izITsThf' => [ 'from' => 'CWgPqdn3YweN', 'message' => 'test message three', 'startedAt' => '2020-07-11 11:20:19', 'subject' => '-MC00BHCZlXUp25C5nlS', 'to' => 'lSUfZ4sgEJd', ], '-MC1kAi1niswXtjY_h4s' => [ 'from' => 'CWgPqdn3YweN', 'message' => 'test message two', 'startedAt' => '2020-07-12 11:19:52', 'to' => 'lSUfZ4sgEJd', ], '-MC1kOtfnIlAYtmJsD-a' => [ 'from' => 'CWgPqdn3YweN', 'message' => 'test message one', 'startedAt' => '2020-07-12 11:18:50', 'to' => 'lSUfZ4sgEJd', ], '-MC1kOtfnIlAhgcufu' => [ 'from' => 'CWgPqdn3YweN', 'message' => 'test message zero', 'startedAt' => '2020-07-12 11:00:50', 'to' => 'YLisXjk07w93', ], ]; function getLatestUniqueConversationMessagesByUser(array $message, string $user): array { $conversations = []; $latestUniqueConversationMessages = []; foreach ($message as $messageKey => $message) { $participants = [$message['from'], $message['to']]; // Skip entries where $user is has not participated (not sure if needed) if (!in_array($user, $participants)) { continue; } // Make "to|from" same as "from|to" sort($participants); $conversationKey = join('|', $participants); // Check if conversation has been handled already if (!array_key_exists($conversationKey, $conversations)) { $conversations[$conversationKey] = true; // Save as "handled" $latestUniqueConversationMessages[$messageKey] = $message; // Save actual data to return } } return $latestUniqueConversationMessages; } var_dump(getLatestUniqueConversationMessagesByUser($data, 'CWgPqdn3YweN'));