Finding records in one table and showing them in a portal in another are two processes that don't have a direct relationship to each other.
The easiest way to show people from A in a portal in B would be to create a cartesian relationship between those tables, put a portal based on that relationship on your layout and filter the portal. But depending on the number of People records, that might be not the best way performance-wise.
Another possibility is to
• create a global text field in your other table, like gNameFilter
• create a calculation field in your people table, say "cFirstLettername", result text, indexed, formula = Left ( nameLast ; 1 )
• define a relationship between table A and B, where the gNameFilter = cFirstLettername
Put a portal on your layout based on that relationship, sort it by nameLast, nameFirst, and use your script to set the desired letter into the global. (Do not write 26 scripts – write one script and pass a script parameter! Or create a related Letters table).
Here's a sample file that may be help you.
FilterPeople_eos.fmp12.zip 18.3 K