Add error messages for minimum required non-NA Values

[SteffenMoritz]

Would be nice, if the package directly gives a error message, when the chosen method is not able to work properly because the time series is too short.

na.interpolation: "need at least two non-NA values to interpolate"
na.kalman: around 3 values + possible infinite loop
na.mean: 1 non NA value
na.locf: 1 non NA value
na.ma: unclear / possible errors for very small inputs (time series of length smaller parameter k)

[FxKu]

My remark fits to this issue:
Due to a mistake in my own code I passed a time series only with NaNs to the na.kalman method. It calls na.locf which contains these lines:

#Replace NAs through locf/nocb from the other direction

else if (na.remaining == "rev") {
   if (option == "locf") {
      data <- na.locf(data, option = "nocb")
   }
   else if (option == "nocb") {
      data <- na.locf(data, option = "locf")
   }
}

I think, this leads to endless calls of na.locf. My error message is:
na.locf(data, option = "nocb") : node stack overflow

Using imputation with an "empty" time series is nonsense, of course. But, as you mentioned in your post, having error message would be nice :)

[SteffenMoritz]

Thanks a lot for your error report.
This specific error was not on my radar yet.

Adding better error messages + improving behavior for these edge cases is definitely on the ToDo list for one of the next updates.

[SteffenMoritz]

Error Messages now present for a lot of wrong inputs.