visnights contains quarterly visitor nights (in millions) from 1998 to 2016 for twenty regions of Australia.
a. Use window( ) to create three training sets for visnights [, "QLDMetro"], omitting the last 1, 2 and 3 years; call these train1, train2, and train3, respectively. For example train1 <- window(visnights[, "QLDMetro"], end $=c(2015,4))$.
b. Compute one year of forecasts for each training set using the snaive() method. Call these $f c 1, f c 2$ and $f c 3$, respectively.
c. Use accuracy() to compare the MAPE over the three test sets. Comment on these.