排名和排序
>> obj = Series(range(4),index=['d','a','b','c'])
>> obj.sort_index()
a 1
b 2
c 3
d 0
dtype: int64
obj.sort_index(by="",)
>> obj = Series(range(4),index=['d','a','b','c'])
>> obj.sort_index()
a 1
b 2
c 3
d 0
dtype: int64
obj.sort_index(by="",)