DAX: Why are duplicate values excluded when calculating an average?

[Anonymous]

I have the following situation: I have a table that assigns a school grade to each student per subject. Then I have a second mapping table that assigns a percentage value (100%, 85%, 75%, 65%, 50%) to each school grade (A, B, C, D, F).

Now I want to calculate the average grade in percent for each school subject. I have already found the following solution:

AverageEnglish = Calculate(average(Percentages[Percentage]),Filter(Grades, (Grades[Subject])="English"))

However, this solution is not correct because I am looking for a measure that calculates the average for each school subject and not just for one specific subject (in this case English). Also, the result is wrong because if two students have the same grade in a subject, the double values are left out of the calculation. See this example where two students have the grade "B" in English:

FormId	Students.Id	Subject	Grade
1	1	English	B
2	2	English	B
3	3	English	D
4	1	Maths	A
5	2	Maths	D
6	3	Maths	B

Subject	AverageEnglish	AverageMaths
English	75%
Maths		83,33%

As you can see above, the result is therefore correct for mathematics but wrong for English. Does anyone have an idea how to solve this problem?

[amitchandak]

@Anonymous , the formula is correct , may be you need

AverageEnglish = Calculate(averagex(values(Table[School]), calculate(Percentages[Percentage])),Filter(Grades, (Grades[Subject])="English"))

Can you share sample data and sample output in table format? Or a sample pbix after removing sensitive data.

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[Anonymous]

Hello!

I tried your measure but unfortunately it gives the same error, so the double values are left out.

I do not know how to share files on this board. But here are my sample tables:

Grades

FormId	Students.Id	Subject	Grade
1	1	English	B
2	2	English	B
3	3	English	D
4	1	Maths	A
5	2	Maths	D
6	3	Maths	B
7	1	French	A
8	2	French	C
9	3	French	B
10	1	Latin	B
11	2	Latin	A
12	3	Latin	F
13	1	Biology	B
14	2	Biology	B
15	3	Biology	A

Percentages

Mapping.Id	Grade	Percentage
Map1	A	100
Map2	B	85
Map3	C	75
Map4	D	65
Map5	F	50

GradeAverage (desired outcome):

English	78,33%
French	86,67%
Latin	78,33%
Maths	83,33%
Biology	90%

Actual wrong result:

Subject	Average
English	75%
French	86,67%
Latin	78,33%
Maths	83,33%
Biology	92,50%

[amitchandak · Accepted solution]

@Anonymous , Please find the attached file after signature.

Two solutions, using new column (then avg) and new measure

  Please provide your feedback comments and advice for new videos
Tutorial Series Dax Vs SQL Direct Query PBI Tips
Appreciate your Kudos.

[Anonymous]

Thank you so much, that is exactly what I was looking for!