Subtract two filtered columns

[OSUATS]

I need a formula to subtract rows of two different columns that are filtered from another sheet. I need to filter out dashes and blanks so that the value can be used in another formula. Below is what I need to calculate, but need to be able to filter. (couldn't find a subtotal formula solution)

=ReportDataTableList[Drop Completed/Canceled Time]-ReportDataTableList[Pick Completed/Canceled Time]

Thanks for any suggestions!