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<?php $rows = [ (object)['group' => 'a', 'other_col' => 'a'], (object)['group' => 'b', 'other_col' => 'a'], (object)['group' => 'a', 'other_col' => 'a'], (object)['group' => 'a', 'other_col' => 'a'], (object)['group' => 'c', 'other_col' => 'a'], ]; $groups = array_count_values(array_column($rows, 'group')); print_r($groups);