熊猫数据框索引在索引数据框的子集时引起问题。 如何删除索引，或防止发生错误？

Question

我有一个数据框x1 。 我制作了数据x1_sub的子集x1_sub ，在这里我需要使用for循环来索引其项。 但是由于子集保留了原始熊猫数据帧的索引，因此其行如下：

x1_sub['words']

1         investment
2               fund
4            company
7              claim
9           customer
20              easy
...              ...

所以，当我做这样的事情来按x1_sub索引x1_sub的行时：

for i in range(len(x1)):
    for j in range(len(x1_sub)):
        if (x1['word'][i]==x1_sub['word'][j]):
            print(i, j)

它给出以下错误：

KeyError                                  Traceback (most recent call last)
<ipython-input-48-e3c9806732a6> in <module>()
      3 for i in range(len(x1)):
      4     for j in range(len(x1_sub)):
----> 5         if (x1['word'][i]==x1_sub['word'][j]):
      6             print(i, j)
      7 

c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\series.py in __getitem__(self, key)
    621         key = com._apply_if_callable(key, self)
    622         try:
--> 623             result = self.index.get_value(self, key)
    624 
    625             if not is_scalar(result):

c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexes\base.py in get_value(self, series, key)
   2558         try:
   2559             return self._engine.get_value(s, k,
-> 2560                                           tz=getattr(series.dtype, 'tz', None))
   2561         except KeyError as e1:
   2562             if len(self) > 0 and self.inferred_type in ['integer', 'boolean']:

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

KeyError: 0

---

编辑：一些示例数据：

以下数据保存在名为example.csv的csv文件中：

word    score
service 1
customer    4
agent   3
product 6
easy    2
claim   2
fast    1
financial   5
information 1
benefit 4
company 3
helpful 6
time    2
future  2
policy  1
health  5
life    1
fund    4
complicated 3
investment  6
join    2
payment 2
premium 1
excellent   5
experience  1
family  4
nice    3
proces  6
satisfactory    2

代码是这样的：

import pandas as pd

x1 = pd.read_csv(r'C:\Users\h473\Documents\Indonesia_verbatims W1 2018\Insurance Data X3\example.csv')

x1_sub = x1[x1['score']<=2]

for i in range(len(x1)):
    for j in range(len(x1_sub)):
        if (x1['word'][i]==x1_sub['word'][j]):
            print(i, j)

这是输出：

0 0
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-63-08d55a712c99> in <module>()
      7 for i in range(len(x1)):
      8     for j in range(len(x1_sub)):
----> 9         if (x1['word'][i]==x1_sub['word'][j]):
     10             print(i, j)

c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\series.py in __getitem__(self, key)
    621         key = com._apply_if_callable(key, self)
    622         try:
--> 623             result = self.index.get_value(self, key)
    624 
    625             if not is_scalar(result):

c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexes\base.py in get_value(self, series, key)
   2558         try:
   2559             return self._engine.get_value(s, k,
-> 2560                                           tz=getattr(series.dtype, 'tz', None))
   2561         except KeyError as e1:
   2562             if len(self) > 0 and self.inferred_type in ['integer', 'boolean']:

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

KeyError: 1

---

编辑2：此外，如果x1_sub是一个列表，则错误是不同的：

import pandas as pd

x1 = pd.read_csv(r'C:\Users\h473\Documents\Indonesia_verbatims W1 2018\Insurance Data X3\example.csv')

#x1_sub = x1[x1['score']<=2]
x1_sub = ['service', 'claim', 'health', 'fund', 'premium', 'nice', 'process']

for i in range(len(x1)):
    for j in range(len(x1_sub)):
        if (x1['word'][i]==x1_sub['word'][j]):
            print(i, j)

产生以下输出：

TypeError                                 Traceback (most recent call last)
<ipython-input-68-dec8c7e33757> in <module>()
      8 for i in range(len(x1)):
      9     for j in range(len(x1_sub)):
---> 10         if (x1['word'][i]==x1_sub['word'][j]):
     11             print(i, j)

TypeError: list indices must be integers or slices, not str

Answer 1

我认为最好避免在熊猫中循环，因为如果存在某些矢量化解决方案，速度会非常慢：

x1_sub  = ['service', 'claim', 'health', 'fund', 'premium', 'nice', 'process']

x2 = x1[x1['word'].isin(x1_sub)]
print (x2)
       word  score
0   service      1
5     claim      2
15   health      5
17     fund      4
22  premium      1
26     nice      3

Answer 2

尝试使用Dataframe.set_index（keys，inplace = True）分配单独的索引，请参阅此文档https://pandas.pydata.org/pandas-docs/stable/generation/pandas.DataFrame.set_index.html