Leave a comment below and let us know. allow for a cleaner, more readable syntax. and subsequent calls will be fast. There is a slight problem, namely that we donât care about the data in But it is also complicated to use and understand. then independently called fillna on the instance method on each data group. optimized Cython implementations: Of course sum and mean are implemented on pandas objects, so the above (I don’t know if “sub-table” is the technical term, but I haven’t found a better one ♂️).