multi-columns in category-num operators #43
Description
when i use operator like groupbythenxxx.d1 is numerical data and d2 is the category data.
if d2 contains one feauture ,for example groupby('date'),it's okay.
however,if d2 contains multi features like groupby(['date','class']) it seems doesn't work.
i've read the codes in FNode, function .calcualte return data[self.name], seems name only support one column.