Measure Request: Value is within TopN, True or False

Hi nckpedersen ,

I created a sample pbix file(see attachment) for you, please check whether that is what you want. 

1. Create two measures as below to judge if the account is Top 2 accounts

Rank = RANKX ( ALLSELECTED ( 'Accounts' ), CALCULATE ( SUM ( 'Accounts'[Sales] ) ) )

Flag = 
VAR _tab =
    CALCULATETABLE (
        VALUES ( 'Accounts'[Account] ),
        FILTER ( 'Accounts', [Rank] <= 2 )
    )
RETURN
    IF ( SELECTEDVALUE ( 'Contacts'[Account] ) IN _tab, 1, 0 )

2. Create a table visual and apply the visual-level filter with the condition(Flag is 1)

If the above one can't help you get the desired result, please provide some sample data in your tables (exclude sensitive data) with Text format and your expected result with backend logic and special examples. It is better if you can share a simplified pbix file. You can refer the following link to upload the file to the community. Thank you.

How to upload PBI in Community

Best Regards