Max Month in Set Analysis

[A_PR]

count(distinct [id])/
(RangeSum(Below(count(distinct [id]),0,(NoOfRows()-RowNo()+1)))+
RangeSum (above(count(distinct [id]),1,(RowNo()-1))))

I have the formula for a graph which is working perfectly fine. I need to add a criteria where this graph only show data of the last month of reference_date.

created a variable: vLastMonth =Month(Max(reference_date))

Count(DISTINCT {<month(reference_date) = {"$(vLastMonth)"}>} [id]) /
(RangeSum(Below(Count(DISTINCT {<month(reference_date) = {"$(vLastMonth)"}>} [id]),0,NoOfRows() - RowNo() + 1)) +
RangeSum(Above(Count(DISTINCT {<month(reference_date) = {"$(vLastMonth)"}>} [id]),1,RowNo() - 1)))

This formula gives error in expression.

Can someone please let me know what am I doing wrong  in this formula?

[MatheusC]

@A_PR 
Previously create a month field in the script

Month(reference_date) -> Month
MonthName(reference_date) -> MonthYear

Or view through a date range

[reference_date]={">=$(=monthstart(max(reference_date)))<=$(=monthend(max(reference_date)))"}

Formatting Date may be necessary depending on the format of your data.

- Matheus