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pandas Series KeyError: -1
前几天写分析方法，遇到的一个错误：
具体我已经在stackoverflow 里面得到了详细的解答，下面我把问题和解决办法总结一下，方便日后的回顾
问题：
sql = "select {}, {} from {} where {};".format(v1, v2, table, where) df = pd.read_sql(sql, app.config.get(‘sqlalchemy_engine‘)) df_dropna = df.dropna() dddd = df_dropna[v2] print type(dddd) print dddd[1] # print dddd # Have the answer print dddd[-1] # keyerror: -1
错误：
File "/usr/lib/python2.7/dist-packages/flask/app.py", line 2000, in __call__ return self.wsgi_app(environ, start_response) File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1991, in wsgi_app response = self.make_response(self.handle_exception(e)) File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1567, in handle_exception reraise(exc_type, exc_value, tb) File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1988, in wsgi_app response = self.full_dispatch_request() File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1641, in full_dispatch_request rv = self.handle_user_exception(e) File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1544, in handle_user_exception reraise(exc_type, exc_value, tb) File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1639, in full_dispatch_request rv = self.dispatch_request() File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1625, in dispatch_request return self.view_functions[rule.endpoint](**req.view_args) File "/opt/code/my_code/app4wp/app/views.py", line 136, in varianc_get print dddd[-1] File "/usr/local/lib/python2.7/dist-packages/pandas/core/series.py", line 601, in __getitem__ result = self.index.get_value(self, key) File "/usr/local/lib/python2.7/dist-packages/pandas/indexes/base.py", line 2169, in get_value tz=getattr(series.dtype, ‘tz‘, None)) File "pandas/index.pyx", line 105, in pandas.index.IndexEngine.get_value (pandas/index.c:3567) File "pandas/index.pyx", line 113, in pandas.index.IndexEngine.get_value (pandas/index.c:3250) File "pandas/index.pyx", line 161, in pandas.index.IndexEngine.get_loc (pandas/index.c:4289) File "pandas/src/hashtable_class_helper.pxi", line 404, in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:8555) File "pandas/src/hashtable_class_helper.pxi", line 410, in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:8499)KeyError: -1
为什么呢？
When you use dddd[-1] it is looking for a column with the -1 key, that does not exist. So, to do index slicing you must use .iloc.
Pandas dataframes work differently from regular python lists,d ictionaries and etc....
哈哈，就这么解决了！！！
print dddd.iloc[-1]
pandas Series KeyError: -1
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