Are you wanting a column that displays all the formats with another field(s) or a custom column that shows how many (number) different formats of a particular book you have?
I created 3 custom columns that I call "Formats", "Location" and "All Formats"(column heading)
"Formats" (created using quick create option)
Code:
Lookup name: formats
Column heading: Formats
Column type: Column built from other columns
Description: eBook Formats available
Template: {formats}
"Location"
Code:
Lookup name: locate
Column heading: Location
Column type: Text, column shown in the Tag browser
Description: Shelf location of physical books or whether it is an Audiobook
Template: {formats}
"All Formats"
Code:
Lookup name: mod_format
Column heading: All Formats
Column type: Column built from other columns
Description: Combines informat from Formats and Location columns
Template: {:'approximate_formats()'} {#locate}
I only display the "All Formats" column. I can quickly glance at the All Formats column to see what format my ebooks are in (AZW(3), EPUB, MOBI, PDB, PDF) or if I also have an audiobook or physical edition also.
Since I started collecting books over 40 years ago I am trying to slowly replace my physical books with audio and ebooks. I love reading physical books but I also enjoy the convenience of carrying ebooks and audiobooks on my phone. Some weeks I will be reading 3 different books depending on where/what I am doing.