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<?php $array = [ ["444", "0081"], ["449", "0081"], ["451", "0081"], ["455", "2100"], ["469", "2100"] ]; $result = []; foreach ($array as $row) { if (!isset($ref[$row[1]])) { $ref[$row[1]] = $row; $result[] = &$ref[$row[1]]; } else { $ref[$row[1]][0] .= ',' . $row[0]; } } var_export($result);

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