factor out yearly_stacked_series
factor out yearly_stacked_series

still memoized with global variable.

joncgoodwin/dfr-browser,joncgoodwin/dfr-browser,agoldst/dfr-browser,agoldst/dfr-browser,agoldst/dfr-browser,joncgoodwin/dfr-browser,altaf-ali/dfr-browser,agoldst/dfr-browser,joncgoodwin/dfr-browser,altaf-ali/dfr-browser,altaf-ali/dfr-browser,joncgoodwin/dfr-browser,altaf-ali/dfr-browser