Please find the attached file where I have done the date selector. Please refer to the screenshot for quarter.
Let me know if this helps.
Thanks and Regards,
date selector.twbx 315.6 KB
This would not be a filter. A filter by definition removes data from the view. What you're asking for is the ability to change the level level of detail in your view. We will do this with two fairly easy to understand tools. You are not looking at just the first day of the month. You are instead looking at the entire month worth of data. What is happening (most likely) in your calculation is that every single data is looked at in the datasource and then using either datepart or DATETRUNC() functions you remove anything after the month (day, minute, hour, second). What this is allowing you to do is plot hundreds maybe thousands of data points that occur somewhere on the timeline as if they all occurred in the same timeframe (month).