I'm no expert but here's a quick tip -
In a recent version of Excel, do format cells, number, custom and from the drop down, select the format that has negative numbers in red. Simply change the "red" to "white" and the -ve numbers are hidden (sort of).
You could use IF to refer to the numbers (which could be in a hidden column) and have, for example, =IF(G11<0,"",G11)in a new column to display the p+ve numbers only - which would do the trick.
Hope that makes sense. No doubt some genius out there will have a better method though!