Filter in DAX formula: only use regular persons to calculate the total average

[Anonymous]

Hi, 

I'm keeping track of the attendance of my sport sessions. I would like to have an overview of everyone's attendance. But to calculate the overall average I only want to take into account individuals who effectively belong to the group in question. 

Some example data: 

Name	sessions	present	attendance	group	primary group
John	102	1	1%	A	B
Arthur	102	73	72%	A	A
Chris	102	60	59%	A	A
Luke	102	2	2%	A	B
David	102	88	86%	A	A

The overall average would be 44%. but because some individuals only participate occasionally in this group they bring the average down tremendously. So I just want to calculate the average of those whose group is equal to their origin group (Arthur, Chris and David in this case). The result would be 72%. 

How can I filter this in a DAX formula? (The primary group column is not present in this table but stands somewhere else!) 

Thank you 

[JorgePinho]

Is the table where the primary group column is connected to the one with the group?

[Anonymous]

yes

[JorgePinho]

I would recommend you to create a flag (1 if groups match, 0 if don't match) calculated column and then use CALCULATE to make an average considering a filter by that column.