title: Error : missing value where TRUE/FALSE needed
body: <pre><code>WEEK PRICE QUANTITY SALE_PRICE TYPE
  1  4992  5.99  2847.50       0.00    3
  2  4995  3.33 36759.00       3.33    3
  3  4996  5.99  2517.00       0.00    3
  4  4997  5.49  2858.50       0.00    3
  5  5001  3.33 32425.00       3.33    3
  6  5002  5.49  4205.50       0.00    3
  7  5004  5.99  4329.50       0.00    3
  8  5006  2.74 55811.00       2.74    3
  9  5007  5.49  4133.00       0.00    3
  10 5008  5.99  4074.00       0.00    3
  11 5009  3.99 12125.25       3.99    3
  12 5017  2.74 77645.00       2.74    3
  13 5018  5.49  5315.50       0.00    3
  14 5020  2.74 78699.00       2.74    3
  15 5021  5.49  5158.50       0.00    3
  16 5023  5.99  5315.00       0.00    3
  17 5024  5.49  6545.00       0.00    3
  18 5025  3.33 63418.00       3.33    3
  </code></pre>
  
  <p>If there are consecutive 0 sale price entries then I want to keep last entry with sale price 0. Like I want to remove week 4996 and want to keep week 4997, I want week 5004 and I want to remove 5002. Similarly I want to delete 5021 &amp; 5023 and want to keep week 5024.</p>