The best I can offer is not quite what you want, but here it is anyway.
You can add calculated values for your default endpoints as follows:
Jan1ThisYear : DATEPARSE('yyyyMMdd',STR(YEAR(today()))+'0101')
DATEPARSE('yyyyMMdd',STR(YEAR(DATEADD('month', -1, today())))+IIF(MONTH(today())>10 OR MONTH(today())=1,'', '0')
+STR(MONTH(DATEADD('month', -1, today())))+'01')
Now, you can drag your date dimension to Filters, choose "Individual Dates", then Condition-By Formula, and type in the formula field the following:
DateDimension>=[Jan1ThisYear] AND DateDimension<=[FirstOfLastMonth]
Unfortunately, the resulting filter won't be a slider. I'm afraid it's not possible to set the endpoints of a slider filter (i.e. ranges) to parameters.
Additionally, to give control to the users to change the default endpoints, you can create parameters out of the calculated fields I described above.
Right-click on Jan1ThisYear, choose Create->Parameter, name it "Range Start". You will see it has the desired default date.
Right-click on FirstOfLastMonth, choose Create->Parameter, name it "Range End". You will see it has the desired default date.
Define your date filter as DateDimension>=[Range Start] AND DateDimension<=[Range End]
You still won't see the date filter as a slider, but you at least see the range endpoints and give the users control to change them.
Hope this helps!
When you create the Range Start and Range End parameters, don't forget to say the allowable values are "All".
Thanks so much for your reply.
Let me check the options you sent and get back to you.