Pandas 查询功能不适用于列名中的空格
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Pandas query function not working with spaces in column names
提问by Bhushan Pant
I have a dataframe with spaces in column names. I am trying to use querymethod to get the results. It is working fine with 'c' column but getting error for 'a b'
我有一个列名中有空格的数据框。我正在尝试使用query方法来获得结果。'c' 列工作正常，但出现 'a b' 错误
import pandas as pd
a = pd.DataFrame(columns=["a b", "c"])
a["a b"] = [1,2,3,4]
a["c"] = [5,6,7,8]
a.query('a b==5')
For this I am getting this error:
为此，我收到此错误：
a b ==5
^
SyntaxError: invalid syntax
I don't want to fill up space with other characters like '_' etc.
我不想用“_”等其他字符填充空间。
There is one hack using pandasql to put variable name inside brackets example: [a b]
有一个使用 pandasql 将变量名放在括号内的技巧：[ab]
采纳答案by Jarno
From pandas 0.25onward you will be able to escape column names with backticks so you can do
从Pandas0.25开始，您将能够使用反引号转义列名称，以便您可以
a.query('`a b` == 5')
回答by jpp
Pandas 0.25+
Pandas 0.25+
As described here:
如上所述这里：
DataFrame.query()andDataFrame.eval()now supports quoting column names with backticks to refer to names with spaces (GH6508)
DataFrame.query()而DataFrame.eval()现在支持引用列名与反引号引用带有空格的名称（GH6508）
So you can use:
所以你可以使用：
a.query('`a b`==5')
Pandas pre-0.25
0.25 之前的Pandas
You cannot use pd.DataFrame.queryif you have whitespace in your column name. Consider what would happen if you had columns named a, band a b; there would be ambiguity as to what you require.
pd.DataFrame.query如果列名中有空格，则不能使用。考虑一下如果您有名为a,b和 的列会发生什么a b；你需要什么会有歧义。
Instead, you can use pd.DataFrame.loc:
相反，您可以使用pd.DataFrame.loc：
df = df.loc[df['a b'] == 5]
Since you are only filtering rows, you can omit .locaccessor altogether:
由于您只是过滤行，因此您可以.loc完全省略访问器：
df = df[df['a b'] == 5]
回答by jezrael
It is not possible yet. Check github issue #6508:
目前还不可能。检查github 问题 #6508：
Note that in reality .queryis just a nice-to-have interface, in fact it has very specific guarantees, meaning its meant to parse like a query language, and not a fully general interface.
请注意，实际上.query只是一个很好的接口，实际上它有非常具体的保证，这意味着它的目的是像查询语言一样解析，而不是一个完全通用的接口。
Reason is for queryneed string to be a valid python expression, so column names must be valid python identifiers.
原因是query需要字符串是有效的 python 表达式，所以列名必须是有效的 python 标识符。
Solution is boolean indexing:
解决方案是boolean indexing：
df = df[df['a b'] == 5]
回答by Simeon Ikudabo
Instead of using the pandas.query function I would create a condition in this case to lookup values and where the condition is True. For example:
在这种情况下，我将创建一个条件来查找值和条件为 True，而不是使用 pandas.query 函数。例如：
import pandas as pd
a = pd.DataFrame(columns=["a b", "c"])
a["a b"] = [1,2,3,5]
a["c"] = [5,6,7,8]
#a.query('a b==5') Remove the query because it cannot lookup columns with spaces in the name.
condition = a['a b'] == 5
print(a['a b'][condition])
output:
3 5
We see that at index 3 your condition evaluates to True (if you want the specific index and not Series of Boolean values).
我们看到，在索引 3 处，您的条件评估为 True（如果您想要特定索引而不是布尔值系列）。
回答by DTT
I am afraid that the query method does not accept column name with empty space. In any case you can query the dataframe in this way:
恐怕查询方法不接受带有空格的列名。在任何情况下，您都可以通过以下方式查询数据框：
import pandas as pd
a = pd.DataFrame({'a b':[1,2,3,4], 'c':[5,6,7,8]})
a[a['a b']==1]
