1

I try to perform some process on all Dataframe I have by using for loop by nothing changes.

Codes:

import pandas as pd

a = pd.DataFrame({'a':[1,2,3,4,5,6,7],
                 'b':[8,9,0,1,2,3,4]})
b = pd.DataFrame({'c':[1,2,3,4,5,6,7],
                 'b':[8,9,0,1,2,3,4]})

li = [a,b]
for i in li:
    'df_{}'.format(i) = i.rename(columns={'b':'test'})

Both a and b outputs:

    a   b
0   1   8
1   2   9
2   3   0
3   4   1
4   5   2
5   6   3
6   7   4

    c   b
0   1   8
1   2   9
2   3   0
3   4   1
4   5   2
5   6   3
6   7   4

Expected output:

    a   test
0   1   8
1   2   9
2   3   0
3   4   1
4   5   2
5   6   3
6   7   4

    c   test
0   1   8
1   2   9
2   3   0
3   4   1
4   5   2
5   6   3
6   7   4

can anyone point out what is wrong here? I try to use it on other dataset but nothing changes and I do not understand why. Please help.

Btw, I am wondering whether if I can make a different name for it like. above edited?

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3 Answers 3

Reset to default
3

Use inplace=True in rename:

for i in li:
    i.rename(columns={'b':'test'}, inplace=True) # Without assignment

Output:

a.head()
   a  test
0  1     8
1  2     9
2  3     0
3  4     1
4  5     2

b.head()
   c  test
0  1     8
1  2     9
2  3     0
3  4     1
4  5     2
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3 Comments

Thank you but I made some changes and wondering you can assist me on it? pls
@Anonymous Making dynamic variable name is simply a bad approach. Many good workaround can be found at How do i create a variable number of variables
Thanks and I try to use globals() but it wont work.
0

rename creates a new instance.

instead try:

for i in li:
    i = i.rename(columns={'b':'test'}, inplace=True)
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1 Comment

Thank you but I made some changes and wondering you can assist me on it? pls
0

(EDIT):

It looks like the columns you're transforming are getting superpositioed on the copied object. The following workaround should solve this:

for i in li:
    f'df_{i}' = i.copy(deep=True)
    f'df_{i}' = f'df_{i}'.rename(columns={'b':'test'})
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2 Comments

Thank you but I made some changes and wondering you can assist me on it? pls
Responded, take a look

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