Measure to group and count rows

Hi TomSinAA ,

First create an enter table:

Then please create this measure:

Count of M-IDs = 
VAR __table = SUMMARIZE('Table1','Table1'[M-ID],'Table1'[S-ID],"@EnteredBy",[Entered By Group])
VAR __c_sid = CALCULATETABLE(VALUES(Table1[S-ID]),FILTER(__table,[@EnteredBy]="C"))
VAR __not_c_sid = CALCULATETABLE(VALUES(Table1[S-ID]),FILTER(__table,[@EnteredBy]<>"C"))
VAR __only_c_count = COUNTROWS(EXCEPT(__c_sid,__not_c_sid))
VAR __not_only_c_count = COUNTROWS(EXCEPT(__not_c_sid,__c_sid))
VAR __result = IF(SELECTEDVALUE('Table'[Grouping])="All S-ID entered by C-group",__only_c_count,__not_only_c_count)
RETURN
__result

Output:

Best Regards,
Gao
Community Support Team

If there is any post helps, then please consider Accept it as the solution  to help the other members find it more quickly.
If I misunderstand your needs or you still have problems on it, please feel free to let us know. Thanks a lot!

How to get your questions answered quickly --  How to provide sample data in the Power BI Forum