#------------
# seasonality
#------------

Read("http://web.pdx.edu/~gerbing/data/seasonality.csv")

# create a time series of the data
F.ts <- ts(Y, start=c(2001,1), frequency=4)
pdf("season_data.pdf", 6, 4)
plot(F.ts)
dev.off()

# autocorrelations and plot by lag
cc <- acf(F.ts)
cc

pdf("season_acf.pdf", 6, 4)
plot(acf(Y))
dev.off()

# seasonal and trend decomposition of time series
decomp <- stl(F.ts, s.window="periodic")
decomp
pdf("season_decomp.pdf", 6, 4)
plot(decomp)
dev.off()

# Holt-Winters exponential smoothing with trend and seasonal components
hw <- HoltWinters(F.ts)
hw
pdf("season_HW.pdf", 6, 4)
plot(hw) 
dev.off()