Background – I have a dataset with two headers that I’ve read from a CSV…
df = pd.read_csv(file, header=[0,1])
print(df)
A B C
a b c
---------------
0 1 2 3
1 4 5 6
2 7 8 9
...
What I Want – I’d like to duplicate one of the columns (say, A) into a new column D, such that…
A B C D
a b c a
----------------------
0 1 2 3 1
1 4 5 6 4
2 7 8 9 7
...
What I’m Getting – …but when I do this using df['D'] = df['A'], what I get is a copy without the content of the second header…
A B C D
a b c
----------------------
0 1 2 3 1
1 4 5 6 4
2 7 8 9 7
...
TLDR – How can I capture the content of the second header of my multi-index dataframe when copying a column?
>Solution :
Need to specify both levels of multiindex
# assign ('A', 'a') values to ('D', 'a') column
df[('D','a')] = df[('A','a')] # or df['D','a'] = df['A']
