I have monthly data and I want to crreat a series that is a ratio of a variable relative to the value of the variable in december the year before, i.e.,
Code: Select all
y_mar_2017 = x_mar_2017 / x_dec_2016
y_feb_2017 = x_feb_2017 / x_dec_2016
y_jan_2017 = x_jan_2017 / x_dec_2016
y_dec_2016 = x_dec_2016 / x_dec_2015
y_nov_2016 = x_nov_2016 / x_dec_2015
what is the best way to create such a y-series?