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<?php $users = [ ['first_name' => 'Bob', 'last_name' => 'Smith'], ['first_name' => 'Steve', 'last_name' => 'Little'], ['first_name' => 'Eric', 'last_name' => 'Fielder'], ['first_name' => 'Steve', 'last_name' => 'Richardson'], ['first_name' => 'Sue', 'last_name' => 'Boy'], ['first_name' => 'Bob', 'last_name' => 'Sanders'], ['first_name' => 'Bob', 'last_name' => 'Sanders'], ['first_name' => 'Bob', 'last_name' => 'Smith'], ]; foreach ($users as $row) { $grouped[$row['first_name']][$row['last_name'][0] ?? ''][$row['last_name']][] = $row; } var_export($grouped); /* foreach ($grouped as $firstName => $leadingLetterGroup) { if () */

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