Output value from Pervious Month (December) in January - powerbi

Question

Hopefully someone can help me.
I use the measure below to output a value from the previous month, however it appears to have broken this month (January).
In March it outputs Februarys value, and in April it outputs Marchs value. However as it is January it doen't appear to be outputting Decembers value.
Can anyone advise how I would adapt this measure to retrieve Decembers value?
Previous Month = var current_month= MONTH(TODAY()) return CALCULATE( AVERAGE('DATA_TABLE'[VALUE]), FILTER(DATA_TABLE,MONTH(DATA_TABLE[DATE])=current_month-1))
Thanks for your support.

Answer 1

Dax's Month commmand returns a number. In your case, you're asking for month 0, as january is month number 1. Since there is no month numbered as 0, it returns no data (blank).
You just need to add a condition for when the month is 0, to instead return data for the previous year's last month.
This is a possible solution:
VAR current_month = MONTH(TODAY())
VAR current_year = YEAR(TODAY())
VAR previous_month = current_month - 1
VAR previous_year = current_year - 1
RETURN
CALCULATE(
AVERAGE('Table'[Values]);
FILTER('Table';
IF(previous_month = 0;
MONTH('Table'[Date]) = 12 && YEAR('Table'[Date]) = previous_year;
MONTH('Table'[DATE]) = current_month - 1)
)
)
This way you accomodate for the 0 month value and filter according to it.
If it is not 0, the measure behaves as before. Otherwise it filters for the last month of the previous year.