I am trying to determine whether there is an entry in a Pandas column that has a particular value. I tried to do this with if x in df['id']. I thought this was working, except when I fed it a value that I knew was not in the column 43 in df['id'] it still returned True. When I subset to a data frame only containing entries matching the missing id df[df['id'] == 43] there are, obviously, no entries in it. How to I determine if a column in a Pandas data frame contains a particular value and why doesn't my current method work? (FYI, I have the same problem when I use the implementation in this answer to a similar question).


当前回答

你可以试着检查一个名为“id”的列中的特定值“x”

if x in df['id'].values

其他回答

或者用级数。tolist或Series.any:

>>> s = pd.Series(list('abc'))
>>> s
0    a
1    b
2    c
dtype: object
>>> 'a' in s.tolist()
True
>>> (s=='a').any()
True

系列。tolist做了一个关于一个系列的列表,而另一个我只是从一个常规系列中获得一个布尔系列,然后检查是否有任何真布尔系列。

你也可以使用pandas.Series.isin,尽管它比s.values中的'a'长一点:

In [2]: s = pd.Series(list('abc'))

In [3]: s
Out[3]: 
0    a
1    b
2    c
dtype: object

In [3]: s.isin(['a'])
Out[3]: 
0    True
1    False
2    False
dtype: bool

In [4]: s[s.isin(['a'])].empty
Out[4]: False

In [5]: s[s.isin(['z'])].empty
Out[5]: True

但是,如果您需要为一个DataFrame同时匹配多个值,这种方法可以更加灵活。

>>> df = DataFrame({'A': [1, 2, 3], 'B': [1, 4, 7]})
>>> df.isin({'A': [1, 3], 'B': [4, 7, 12]})
       A      B
0   True  False  # Note that B didn't match 1 here.
1  False   True
2   True   True
found = df[df['Column'].str.contains('Text_to_search')]
print(found.count())

find .count()将包含匹配数

如果它是0,那么意味着字符串没有在列中找到。

使用query()查找符合条件的行,并获得形状为[0]的行数。如果存在至少一个条目,则此语句为True:

df.query('id == 123').shape[0] > 0

Series的in检查该值是否在索引中:

In [11]: s = pd.Series(list('abc'))

In [12]: s
Out[12]: 
0    a
1    b
2    c
dtype: object

In [13]: 1 in s
Out[13]: True

In [14]: 'a' in s
Out[14]: False

一种选择是查看它是否为唯一值:

In [21]: s.unique()
Out[21]: array(['a', 'b', 'c'], dtype=object)

In [22]: 'a' in s.unique()
Out[22]: True

或者一个python集合:

In [23]: set(s)
Out[23]: {'a', 'b', 'c'}

In [24]: 'a' in set(s)
Out[24]: True

正如@DSM所指出的,直接在值上使用in可能更有效(特别是如果你只对一个值执行此操作):

In [31]: s.values
Out[31]: array(['a', 'b', 'c'], dtype=object)

In [32]: 'a' in s.values
Out[32]: True