Dax Calculating Same time previous period with nonstandard periods

Question

I need help dealing with prior period calculations where the periods are not standard.
In our business we define these time periods based on 8 to 10 week periods that really have no correlation to standard weeks, months or quarters.  Additionally there may be some time between these periods that are not defined. For example:
Period 1 (p1) = June 18 - Sept 2
Period 2 (p2) = Sept 17 - Dec 9
The length of the periods are variable and when one ends another does not necessarily begin.
I need to figure out how to compare the sum of a metric in Period 2 with the sum of a metric in Period 1.
I have a standard Date dimension. And I have a period deminsion with the period labels (p1, p2 etc.) the start date, the end date of the periods, and a column called previousPeriod that has the label of the prior period.
Each Fact has a Period ID so that I can use period as a dimension.One of my measures is Sum(sales).
I want it so that if I am viewing the Tabular cube by period, I can have the sum of sales for that period, and the prior one. I hope it is clear what I am trying to do.

Answer 1

You should add to your Date table a column that contains an incremental number for each period, then write something like:
        CALCULATE
            [Sales],
            ALL
( 'Date' ),
            FILTER
                ALL
( 'Date'[IncrementalPeriod] ),
                'Date'[IncrementalPeriod]
                    =
EARLIER ( 'Date'[IncrementalPeriod]
) - 1
I suggest you this pattern that will be published on March 31 - it contains many more examples, including how to write the make this formula working also with a partial arbitrary selection of days in the selected period:
http://www.daxpatterns.com/time-patterns
Marco Russo http://www.sqlbi.com http://www.powerpivotworkshop.com http://sqlblog.com/blogs/marco_russo