use a list plus some strings to select columns from a dataframe

Question

I am trying to make a dynamic list and then combine it with a fixed string to select columns from a dataframe:

import pandas as pd

df = pd.DataFrame([], columns=['c1','c2','c3','c4'])

column_list= ['c2','c3']

df2 = df[['c1',column_list]]

but I get the following error:

TypeError: unhashable type: 'list'

I tried a dict as well but that is similar error.

mozway · Accepted Answer · 2022-12-13 13:17:35Z

2

In your code, pandas tries to find the column ['c1','c2','c3','c4'], which is not possible as only hashable objects can be column names. Even if this wasn't triggering an error (e.g. if you used tuples), this wouldn't give you what you want. You need a 1D list.

Use expansion:

df[['c1', *column_list]]

Or addition:

df[['c1']+column_list]

Output:

Empty DataFrame
Columns: [c1, c2, c3]
Index: []

answered Dec 13, 2022 at 13:17

mozway

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