Is there a way to force seasonality from auto.arima

Question

With the forecast package, I have a time series that I would like ?auto.arima to automatically pick the orders but I would like to coerce seasonali

Answer 1

You can set the D parameter, which governs seasonal differencing, to a value greater than zero. (The default NA allows auto.arima() to use or not use seasonality.) For example:

> set.seed(1)
> foo <- ts(rnorm(60),frequency=12)
> auto.arima(foo)
Series: foo 
ARIMA(0,0,0) with zero mean     

sigma^2 estimated as 0.7307:  log likelihood=-75.72
AIC=153.45   AICc=153.52   BIC=155.54
> auto.arima(foo,D=1)
Series: foo 
ARIMA(0,0,0)(1,1,0)[12]                    

Coefficients:
         sar1
      -0.3902
s.e.   0.1478

sigma^2 estimated as 1.139:  log likelihood=-72.23
AIC=148.46   AICc=148.73   BIC=152.21