na.interp: Interpolate missing values in a time series
Uses linear interpolation for non-seasonal series. For seasonal series, a
robust STL decomposition is used. A linear interpolation is applied to the
seasonally adjusted data, and then the seasonal component is added back.
na.interp(x, lambda = NULL)
Box-Cox transformation parameter. If lambda="auto",
then a transformation is automatically selected using BoxCox.lambda.
The transformation is ignored if NULL. Otherwise,
data transformed before model is estimated.
A more general and flexible approach is available using na.approx in
the zoo package.