Pandas: From SettingWithCopyWarning to loc and iloc

Question

I tried to do:

input1['Signature_Fixed'] = 'NONE' 
i = 0

for row in input1['Signature']:
  if (row == 'Competitor'):
    input1['Signature_Fixed'][i] = input1['brand'][i]
  else:
    input1['Signature_Fixed'][i] = input1['Signature'][i]
  i = i + 1

When I am doing on 1K rows, it works but I have SettingWithCopyWarning then when I am doing on 2M rows, is not working.

Could you please help me to fix that and maybe to convert it with loc/iloc?

Did this question help? https://stackoverflow.com/questions/20625582/how-to-deal-with-settingwithcopywarning-in-pandas — Jarad, Jan 11 '19 at 10:16
Do you want to set brand value where the row is `competitor`? — Mohit Motwani, Jan 11 '19 at 10:18

score 0 · Accepted Answer · answered Jan 11 '19 at 10:18

input1['Signature_Fixed'][i] represents chained indexing, which is explicitly discouraged in the official documentation. Avoid it wherever possible.

In this case, you can avoid for loops altogether by using pd.Series.mask:

bool_mask = df['Signature'] == 'Competitor'
df['Signature_Fixed'] = df['Signature'].mask(bool_mask, df['brand'])

The idea in syntax terms is to operate on columns in vectorised fashion rather than on row-wise loops.

Pandas: From SettingWithCopyWarning to loc and iloc

1 Answers1