I would like to seasonally adjust data series that cannot be negative. How I could do this? Currently I am using seas in R. Is it possible to constrain the output series to 0 or positive values?
It is not very clear what you want exactly, but here are two options that may help you:
Option 1, offsetting: Subtract min(seriesX) from each element of output seriesX;
seriesX[, value := value - min(value)]
Option 2, thresholding: Transform each seriesX element smaller than 0 - to 0
seriesX[value < 0, value := 0]