Tableau - weekly average from daily data

Question

Using Tableau 8.1.
Daily data like this:

Date     Sales
1-1-14     $5
1-2-14     $2
...
6-15-14    $15

Which can be aggregated to weeks of course

Week 1   $15
Week 2   $12
Week 3   $10
Week 4   $13

etc.

I would like to get the weekly average of each month
So like this:

          Weekly Average
Month 1     (weekly average of the weekly total sales)  ($15+$12+$10+13)/4 = 12.5
Month 2 
Month 3 

Does that make sense? If ou simply put "average" in the tableau table, it gives the average daily value PER WEEK (or month) < - I don't want that. I want the average of the weekly totals per month.

Chert

Answer 1

This can be done very simply with one calculated field.

WINDOW_AVG(SUM([Sales]))

Then drag your Date pill onto the rows shelf twice, one aggregated to day, the other to week. Make sure pills are set to discrete (blue) and drag your Sales measure onto the shelf, also as discrete.

Alviani

Answer 2

Quite simple, actually. Create these calculations

Unique Weeks = COUNTD(DATEPART('week',[Date]))
Weekly Average = sum([Sales])/[Unique Weeks]

Then simply report Weekly Average x Month (or Quarter or Year, etc.)
(Note: Some weeks have < 7 days).

Chert