pandas 使用查询函数检查列是否为空
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pandas check if column is null with query function
提问by user2671057
I have pandas dataframe that I want to execute on it query function with isnull() or not isnull() condition like that:
我有 Pandas 数据框，我想用 isnull() 或 not isnull() 条件在它上面执行查询函数，如下所示：
In [67]: df_data = pd.DataFrame({'a':[1,20,None,40,50]})
In [68]: df_data
Out[68]: a
0 1.0
1 20.0
2 NaN
3 40.0
4 50.0
if I use this command:
如果我使用这个命令：
df_data.query('a isnull', engine='python')
or this command:
或此命令：
df_data.query('a isnull()', engine='python')
I get an error:
我收到一个错误：
In [75]: df_data.query('a isnull', engine='python')
File "<unknown>", line 1 a isnull
SyntaxError: invalid syntax
In [76]: df_data.query('a isnull()', engine='python')
File "<unknown>", line 1 a isnull ()
SyntaxError: invalid syntax
What is the right way to do that?
这样做的正确方法是什么？
Thank you.
谢谢你。
回答by jezrael
Use .:
使用.：
a = df_data.query('a.isnull()', engine='python')
print (a)
a
2 NaN
b = df_data.query('a.notnull()', engine='python')
print (b)
a
0 1.0
1 20.0
3 40.0
4 50.0
You can use also logic NaN != NaN:
您还可以使用逻辑NaN != NaN：
a = df_data.query('a != a')
print (a)
a
2 NaN
b = df_data.query('a == a')
print (b)
a
0 1.0
1 20.0
3 40.0
4 50.0
