Filter Album tags to see one row for each different Album tag

Hello everybody,
I have thousands of folders named AlbumArtist-Album, one folder, one album; in case of multicd the folder name is AlbumArtist-Album CDx.

Foobar showed me a little mismatch: the number of Albums is higher than the number of folders.
I imagine that it is possible only if the Album tag of some songs is slightly different.

By the way, how can I filter the Album tags in order to see one row for each different Album tag?
I hope to be clear enough.

Thank you very much for your support

As MP3tag does not compare data of different files, no grouping is possible.
You have to find criteria that can be seen file by file.
So if you have the string from ALBUM in the path somewhere, you could filter for files where this is not so.
"$ifgreater($strstr(%_path%,%album%),0,yes,no)" IS no

Since my folder name is tipically: C:\Music\The Beatles - A Hard Days Night, I need to check if the Album name after the "-" is equal to the content of the %Album% field, both for number of charachters and possibly, for lowercase and uppercase.
In your opinion could be possible?
Many thanks

... and if the data in ALBUM does not contain any invalid characters for folder names...

The function $strstr() already checks if a string is part of another string. So you do not have to specify the part following the -.
Also, I doubt that Windows will allow different folders if only the character case varies.
As I don't know in what respect you see a difference between the number of folders and albums, I would check if there are albums that have the same name like e.g. "gold" oder "Greatest" ...

I've just tested your expression and it works fine for my purpose.
Windows shows me 10226 folders, that is 10236 CDs, all accurately tagged with Mp3Tag.
The strange thing is that Foobar counts correctly 10236 folders, but looking at folders Album tag, shows me 10245 Albums (or CDs); so, I imagine, somewhere there are 19 Album tags wrong.
Your expression will help me to investigate better.
Many thanks for your support and your suggestion.