How to access MultiIndex column after groupby in pandas?
Adding a comma after your ('c','b') tuple seems to work:
df.groupby([('c','a')])[('c','b'),].sum()I'm guessing that without the comma, pandas is just interpreting them as separate items.
Maybe this helps explain the syntax:
df.groupby([('c','a')]).sum() c d b a b(c, a) 2 11 4 114 15 8 15df.groupby([('c','a')])[('c','b'),('d','b')].sum() c d b b(c, a) 2 11 114 15 15