class node python_值错误：对象类型

import pandas as pd

import numpy as np

from datetime import datetime

data = {'date': ['1998-03-01 00:00:01', '2001-04-01 00:00:01','1998-06-01 00:00:01','2001-08-01 00:00:01','2001-05-03 00:00:01','1994-03-01 00:00:01'],

'node1': [1, 1, 2,2,3,2],

'node2': [8,316,26,35,44,56],

'weight': [1,1,1,1,1,1], }

df2 = pd.DataFrame(data, columns = ['date', 'node1','node2','weight'])

df2['date'] = pd.to_datetime(df2['date'])

l1 = [1990,1991,1992,1993,1994,1995,1996,1997,1998]

l2 = [1999,2000,2001]

ndf = df2[df2['date'].dt.year.isin(l1+l2)]

mask = ndf.groupby('node1','node2').apply(lambda x : (x['date'].dt.year.isin(l1)).any())

mask2 = ndf.groupby('node1','node2').apply(lambda x : (x['date'].dt.year.isin(l2)).any())

我得到的错误-Traceback (most recent call last):

File "datanew.py", line 32, in

mask = ndf.groupby('node1','node2').apply(lambda x : (x['date'].dt.year.isin(l1)).any())

File "C:\Python27\lib\site-packages\pandas\core\generic.py", line 5159, in groupby

axis = self._get_axis_number(axis)

File "C:\Python27\lib\site-packages\pandas\core\generic.py", line 357, in _get_axis_number

.format(axis, type(self)))

ValueError: No axis named node2 for object type

我已经在数据中定义了列“node2”，但错误仍然是说node2没有轴。似乎是什么问题？