In my model there is also such dimension as Period. I want to filter the model for 3 chosen months in a row. So if I choose, let's say, '9/1/2019','8/1/2019','7/1/2019', I receive the correct result based on formula above.
But I want to receive the same answer clicking only on 1 month (so, if I click on '9/1/2019', I should get answer based on formula above, but for this month and 2 months before, inclusive, like this: '9/1/2019','8/1/2019','7/1/2019').
I believe you would suggest me to use set expression, so please keep in mind that I have another filter with dimension Medicine_Key and its' filters should be taken into account.