Like operation in loop

Hi All

I am passing to date and from date as input and fetching records from ekko into lt_ekko.

Now ,i had field 'customername' in output screen(importing parameter of a  function module).

LT_ekko has field verkf (customername) values as SDN SAP - 10 records.and SAP - 10 records and SDN - 10 records

My query is if the user gives input as SAP.i need to display SDN SAP records(along with SAP records) and delete SDN records from lt_ekko as it is my final table.

I am giving ranges

IF iv_customername IS NOT INITIAL.

    ls_r_custname-sign = 'I'.

    ls_r_custname-option = 'NP'.

    ls_r_custname-low = iv_customername.

    APPEND ls_r_custname TO lt_r_custname.

  ENDIF.

DELETE lt_ekko WHERE verkf IN lt_r_custname.

this delete statement is not working ,not deleting entries of SDN records.

Thanks

Vamsi