How to change the values of array from a dataframe in Python?

Question

I have an array called arr1

arr1 
Out[23]: 
[('001',
  '249',
  '580',
  'E930'),
 ('001',
  '270',
  '290',
  '780'),
 ('030',
  '110',
   '789',
  '990',
  '996',
  'E8779',
  'E9349',
  'V10',
  'V85'),
 ('030',
  '070',
  '249',
  '270',
  '360',
  '400',
  '450',
  '490',
  'V10',
  'V40'),
 ('400', '580', '990', '916'),
 ('030',
  '270',
  '600',
  '725',
  '780',
  '990',
  '996',
  'V10'),
 ('110',
  '200',
  '249',
  '340',
  '400',
  '410',
  '420',
  '510'),
 ('400', '430'),
 ('210', '400', '420', '450', '720', 'V10'),
 ('070', '280', '286', '290', '300', '450', '570')]

and I have a dataframe called df_map

df_map
Out[24]: 
             Old        New

1             001       A91
2             780       B63
3             E8779     C72
4             V85       D02
5             450       E82
            ...       ...  
999            070      F28

I want to swap Old values in the array with the new values in the dataframe

Here is my code

for x in arr1:
    for y in x:
        y=df_map[(df_map["Old"]==y)]["New"]

but when I check arr1 values they still the orginal

I want arr1 values to be the new values in df_maps

"I check arr1 values they still the original" makes it seem like you're trying to replace the values in arr1. — Henry Ecker
– Henry Ecker ♦, Commented Apr 25, 2021 at 0:56

Nick · Accepted Answer · 2021-04-25 01:23:32Z

3

This can be done by converting your dataframe into a dictionary, then just mapping a function which replaces from the dictionary over each tuple in the list:

df_map = pd.DataFrame({'Old': ['001', '780', 'E8799', 'V85', '450', '070'], 
                       'New': ['A91', 'B63', 'C72',   'D02', 'E82', 'F28']})
arr1 = [
 ('001', '430'),
 ('210', '780', '420', '450', 'E8799', 'V10'),
 ('070', 'V85', '286', '290', '780', '450', '570')
]

m = df_map.set_index('Old')['New'].to_dict()
out = [tuple(map(lambda v:m.get(v, v), t)) for t in arr1]

Output:

[
 ('A91', '430'),
 ('210', 'B63', '420', 'E82', 'C72', 'V10'),
 ('F28', 'D02', '286', '290', 'B63', 'E82', '570')
]

edited Apr 25, 2021 at 1:23

answered Apr 25, 2021 at 1:14

Nick

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