@Fed17 - In your last post you are trying to filter a list of strings using a numbers. This will only return null values. See image below:
With filter masks you want two lists of equal size. One with your data and another of Booleans. You then use the booleans to filter the data list into two outputs. Essentially into true values and false values
See below:
Hope that help explain those two issues.
In regards, maybe try this:
