syntax of redundant data.

data :Begin of I_data

data1,

data2,

data3,

end of i_data

I have a internal table I_dat filled with

data1 data2 data3

1) x y z

2) x y z

3) x y i

4) c n o

5) c n o

6) n p l

7) j k o

8) b l n

9) b l n

10) j k y

I would like to have only lines which are repeating I would like to have lines 1,2,4,5,8,9.

Any idea how could I do.

Best Regards,

Mark