OK I have a Master Table of shipments, and a separate Charges table. There are millions of records in each, and it's come into Filemaker from a legacy system, so all the fields are defined as Text even though they may be Date, Number, etc.
There's a date field in the charges table. I want to create a number field to represent just the year. I can use the Middle function to parse the field and get just the year in a Calculation field. But wouldn't it be faster to have the year as a literal number field, especially since I'm going to be filtering and sorting? So how do I turn this calculation into its value? I've tried just changing the Calculation field to Number, but it just renders blanks.
There's something wrong with your calculation, it should not turn blank just because field type is different. I.e.:
Middle("10-12-2010", 7, 4)
should suffice, provided the calc result is set to Number. You may also wrap it into GetAsNumber(...), but, really, there's no difference as long as field type is right.
If you have FM Advanced, try to set up your calc in the Data Viewer (Tools -> Data Viewer) rather than in Define Fields, this would be faster and, once you like the result, you can transfer it into a field or make a replace. But, from the searching/sorting standpoint there's no difference between a (stored) calculation and a regular field, so replacing is pointless and, actually, more dangerous, as there's no way to undo a wrong replace.