You need to convert your MonthName field to a dual date format. Something like this will do it
LOAD Brand,
Date#(MonthName, 'MMM-YY') As MonthName,
Value
INLINE
[
Brand, MonthName, Value
...
Now for the last 6 months, you can use AddMonths in a set expression, like this:
SUM({<MonthName = {">$(=Date(AddMonths(MonthName, -6), 'MMM-YY'))"}>} Value)
And you should sort the field numerically.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
