In my sales reports, I want to create a table to compare each month relative, so in X dimension it should show months (without a year linked to it) and in Y dimension it should show years (this filter already exists).

         2014    2015    2016 ...

Jan    xxx      xxxx         xxx

Feb  xxx      xxxx       xxx

March

...

In a next step, I would like the months to be cumulative (ie. Jan  = Jan; Feb = Jan+Feb, ...)

I assume I have to create a custom filter for this? I can't seem to find relevant documentation on how to set this up, can anyone show me in the right direction?