how to replace an entire column on Pandas.DataFrame

Question

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?

Answer 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

Answer 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'])