Hi, I was wondering if it would be possible to add an argument to the aggreagte function to retain NA by categories?(default can not to in order to avoid breaking code) Please see below example: df = iris df$Species[5] = NA aggregate(`Petal.Width` ~ Species, df, sum) # does not include NA aggregate(`Petal.Width` ~ addNA(Species), df, sum) # include NA data.table and dplyr include NA by default. Python pandas has an aggreagate function inspired by base R aggregate. An option has been added to include NA. Thank you Best regards Morgan [[alternative HTML version deleted]]