how to replace an entire column on Pandas.DataFrame

I would like to replace an entire column on a Pandas DataFrame with another column taken from another DataFrame, an example will clarify what I am looking for

import pandas as pd
dic = {'A': [1, 4, 1, 4], 'B': [9, 2, 5, 3], 'C': [0, 0, 5, 3]}
df = pd.DataFrame(dic)

df is

'A' 'B' 'C'
 1   9   0
 4   2   0
 1   5   5
 4   3   3

Now I have another dataframe called df1 with a column "E" that is

df1['E'] = [ 4, 4, 4, 0]

and I would like to replace column "B" of df with column "E" of df1

'A' 'E' 'C'
 1   4   0
 4   4   0
 1   4   5
 4   0   3

I tried to use the .replace() method in many ways but I didn't get anything good. Can you help me?

Solution 1:

If the indices match then:

df['B'] = df1['E']

should work otherwise:

df['B'] = df1['E'].values

will work so long as the length of the elements matches

Solution 2:

If you don't mind getting a new data frame object returned as opposed to updating the original Pandas .assign() will avoid SettingWithCopyWarning. Your example:

df = df.assign(B=df1['E'])

Solution 3:

For those that struggle with the "SettingWithCopy" warning, here's a workaround which may not be so efficient, but still gets the job done.

Suppose you with to overwrite column_1 and column_3, but retain column_2 and column_4

columns_to_overwrite = ["column_1", "column_3"]

First delete the columns that you intend to replace...

original_df.drop(labels=columns_to_overwrite, axis="columns", inplace=True)

... then re-insert the columns, but using the values that you intended to overwrite

original_df[columns_to_overwrite] = other_data_frame[columns_to_overwrite]