Set Analysis based on Dimension

[Brites]

Hello!

I am trying to build a table with the following format

YEAR_MONTH	SALES	LAST_YEAR_SALES
OUT 2021	60	40
NOV 2021	50	30
DEC 2021	20	40
JAN 2022	10	10

Where "YEAR_MONTH" is a dimension and SALES is SUM(SALES)

How do i create the "Last Year Sales" columns? I think i would need to perform some kind of set analysis based on the table's dimension. How could i do that, knowing that YEAR_MONTH is a string?

[tm_burgers]

I think firstly you need to add the date field in the data - convert the string into a date. 

Date(Date#(YEAR_MONTH,'MMM YYYY')) as SalesDate