PowerBI - Average and Variance Calculation with conditions - powerbi

Question

I am trying to calculate Variance and Average in PowerBI. I am running into Circular dependency errors.
This is my Data,
Month Year Item Count
1 2017 Chair 100
1 2017 Chair 200
1 2017 Chair 300
1 2017 Bench 110
1 2017 Bench 140
1 2017 Bench 150
2 2017 Chair 180
2 2017 Chair 190
2 2017 Chair 250
2 2017 Bench 270
2 2017 Bench 370
3 2017 Chair 120
3 2017 Chair 150
3 2017 Bench 180
3 2017 Bench 190
4 2017 Chair 200
4 2017 Chair 210
4 2017 Bench 220
4 2017 Bench 230
.
.
.
Average = Sum of Counts for the Previous 3 months / 3
Variance = (Average - Sum(CurrentMonth)) / Average
So, because the average won't be meaningful for the first 3 months, I wouldn't be worried about that.
Expected Output,
Month Year Item Sum(CurrentMonth) Average Variance
1
1
2
2
3
3
4 2017 Chair 410 497 0.21
4 2017 Bench x y z
Lets Say for Chair,
Sum of Current Month = 200 + 210 = 410
Average of Last 3 Months = (100 + 200 + 300 + 180 + 190 + 250 + 120 + 150 )/ 3 = 1490 / 3 = 497
Variance = (497 - 410) / 410 = 87 / 410 = 0.21
Kindly share your thoughts.

Answer 1

I started with this as Table1 (I added a couple months data to yours):
I loaded it into Power BI and added a column called "YearMonth" using this code: YearMonth = Table1[Year]&FORMAT(Table1[Month],"00") ...to get this:
Then I added another column called "Sum(CurrentMonth)" using this code: Sum(CurrentMonth) = SUMX(FILTER(FILTER(Table1,Table1[Item]=EARLIER(Table1[Item])),VALUE(Table1[YearMonth])=VALUE(EARLIER(Table1[YearMonth]))),Table1[Count]) ...to get this:
Then I added another column called "Average" using this code: Average = SUMX(FILTER(FILTER(FILTER(Table1,Table1[Item]=EARLIER(Table1[Item])),VALUE(Table1[YearMonth])<=VALUE(EARLIER(Table1[YearMonth]))-1),VALUE(Table1[YearMonth])>=VALUE(EARLIER(Table1[YearMonth]))-3),Table1[Count])/3 ...to get this:
Lastly, I added a column called "Variance" using this code: Variance = (Table1[Average]-Table1[Sum(CurrentMonth)])/Table1[Sum(CurrentMonth)] ...to get this:
I hope this helps you.