Updating columns in list of pandas dataframe

Question

I am having a list of pandas dataframes. I would like to filter out columns at each dataframe in for loop.

import pandas as pd
df_list=[]
sales = [('Jones LLC', 150, 200, 50),
        ('Alpha Co', 200, 210, 90),
        ('Blue Inc', 140, 215, 95)]
labels = ['account', 'Jan', 'Feb', 'Mar']

df_list.append(pd.DataFrame.from_records(sales, columns=labels))
sales = [('Jones LLC', 122, 566, 345),
        ('Alpha Co', 200, 210, 652),
        ('Blue Inc', 140, 215, 788)]
labels = ['account', 'Jan', 'Feb', 'Mar']
df_list.append(pd.DataFrame.from_records(sales, columns=labels))

col_list = [col for col in df_list[0].columns if col.startswith('acc') or col.startswith('mar')]

#this works
df_list[0]=df_list[0][col_list]
print(df_list[0])

#this does not work
for frame in df_list:
    frame = frame[col_list]
print(df_list[1])

Why doesn't for loop work?

sacuL · Accepted Answer · 2018-09-08 16:33:54Z

1

Because your loop doesn't actually re-assign anything in df_list, it just iterates through. You can do:

for i, frame in enumerate(df_list):
    df_list[i] = frame[col_list]

Which works:

>>> df_list[0]
     account
0  Jones LLC
1   Alpha Co
2   Blue Inc
>>> df_list[1]
     account
0  Jones LLC
1   Alpha Co
2   Blue Inc

answered Sep 8, 2018 at 16:33

sacuL

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