how to delete datawindow row by loop?

I try to go through datawndow rows by for loop and delete those rows I found with condition.  Something like:

For i = 1 to dw_1.RowCount()

....

  if expression then 

    dw_1.DeleteRow(i)

  end if

Next

Looks like not working properly. if DeleteRow dynamically change RowCount()? how to resolve this problem?