df.rename does not alter df column names, but df.columns and df.set_axis do (Pandas)

Question

I have a pandas dataframe that I want to rename the columns on

When I run:

df.rename(columns={0:"C", 1:"D"}, inplace=True)

No change happens, it’s still the original column names.
But if I do:

df.columns = ["C", "D"]

or

df.set_axis(["C", "D"],axis=1, inplace=True)

It works.

Why does not df.rename work?

NOTE: I specifically would like to rename the first and second column regardless of what their name is, it may change (in my case) so I can’t specify it.

Example:

df = pd.DataFrame({"A": pd.Series(range(0,2)),"B": pd.Series(range(2,4))})
df
    A   B
1   0   2
2   1   3

df = pd.DataFrame({"A": pd.Series(range(0,2)),"B": pd.Series(range(2,4))})
df.rename(columns={0:"C", 1:"D"}, inplace=True)
df
    A   B
1   0   2
2   1   3

df = pd.DataFrame({"A": pd.Series(range(0,2)),"B": pd.Series(range(2,4))})
df.columns = ["C", "D"]
df
    C   D
0   0   2
1   1   3

df = pd.DataFrame({"A": pd.Series(range(0,2)),"B": pd.Series(range(2,4))})
df.set_axis(["C", "D"],axis=1, inplace=True)
df
    C   D
0   0   2
1   1   3

EDIT:

My original dataframe had the column names 0 and 1 which is why df.rename(columns={0:"C", 1:"D"}, inplace=True) worked.

Example:

df = pd.DataFrame([range(2,4), range(4,6)])
df
    0   1
0   2   3
1   4   5

df.rename(columns={0:"C", 1:"D"}, inplace=True)
df
    C   D
0   2   3
1   4   5

Asked By: Joachim Spange

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Source

Answer 1

If you don’t want to rename by using the old name, you could zip the current columns and pass in the number of items you want.

If you’re using Python 3.7+ then order should be preserved

Also don’t use inplace=True

print(df)

   A  B
0  0  2
1  1  3

df.rename(columns=dict(zip(df.columns, ['C','E'])))

   C  E
0  0  2
1  1  3

df.rename(columns=dict(zip(df.columns, ['E'])))

   E  B
0  0  2
1  1  3

Answered By: Umar.H

df.rename does not alter df column names, but df.columns and df.set_axis do (Pandas)

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