Pandas query function not working with spaces in column names

Question

I have a dataframe with spaces in column names. I am trying to use query method to get the results. It is working fine with 'c' column but getting error for 'a b'

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:

a b ==5
  ^
SyntaxError: invalid syntax

I don't want to fill up space with other characters like '_' etc.

There is one hack using pandasql to put variable name inside brackets example: [a b]

Solution 1

From pandas 0.25 onward you will be able to escape column names with backticks so you can do

a.query('`a b` == 5') 

Solution 2

Pandas 0.25+

As described here:

DataFrame.query() and DataFrame.eval() now supports quoting column names with backticks to refer to names with spaces (GH6508)

So you can use:

a.query('`a b`==5')

Pandas pre-0.25

You cannot use pd.DataFrame.query if you have whitespace in your column name. Consider what would happen if you had columns named a, b and a b; there would be ambiguity as to what you require.

Instead, you can use pd.DataFrame.loc:

df = df.loc[df['a b'] == 5]

Since you are only filtering rows, you can omit .loc accessor altogether:

df = df[df['a b'] == 5]

Solution 3

It is not possible yet. Check github issue #6508:

Note that in reality .query is 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.

Reason is for query need string to be a valid python expression, so column names must be valid python identifiers.

Solution is boolean indexing:

df = df[df['a b'] == 5]

Solution 4

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:

import pandas as pd
a = pd.DataFrame({'a b':[1,2,3,4], 'c':[5,6,7,8]})
a[a['a b']==1]

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Comments

[Pablo Adames]

Simple and easy, great solution. Thanks!

[Alexey K.]

also if a column has a string number '1', we need ``: a.query(' ` 1 ` == 5')