KB9585: How to create a Year to Day expression using an Applysimple function in MicroStrategy Developer

In certain circumstances it is desirable for business purposes to compare data for one year ago on a day of the week basis (i.e., Tuesday should line up with a Tuesday one year ago).
 
Simply subtracting 365 days, however, will skew the data as it fails to take into account either leap years, or the fact that one year ago today does not fall on the same day of the week. There are database functions which can perform this calculation, but there is also a way to force Strategy to perform this calculation.
 
The following procedure describes how to achieve this:
 

1. Create a new attribute, based off of the table containing data for both the relevant day(s), and the previous year (for this example, the column will be named "Day").
2. In this attribute, create an applysimple with the following expression:
   ApplySimple("#0-364", Day)
   
3. For more information on creating an applysimple, refer to Strategy Knowledge Base document, KB5700-007-0113 - How to implement attribute form expression using Apply Functions in Strategy Desktop.
    
   

Since there are 7 days in each week and 52 weeks in each year, this calculation will always match each day of the week to the appropriate week of the previous year regardless of leap years.
 
NOTE: As each database handles the formatting of dates slightly differently, this exact syntax may not be appropriate. A database administrator should be able to provide the correct syntax for a given database.