How to filter out multiple values?

[Cammagno]

Hi!
I've a 'Category' field that can have a single value or multiple values.
I want a dataview list that only shows the single values of the Category field, so I tried with this:

LIST WITHOUT ID Category
FROM "Folder"
WHERE !NotShow AND typeof("Category")!="array"
GROUP BY Category

but it didn't work (it also shows the multiple values).

How can I filter the multiple values out? TIA for your help!

EDIT: solved, I simply had to remove the " from "Category"... dumb me!