How to solve SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame

Asked Jun 17 '21 at 10:50

Active Jun 17 '21 at 10:50

Viewed 14 times

I have two dfs and trying to create a new colum df1['Conv_Amount'] by dividing df1['Amount'] by df2['Conv_Value'] if df1['Curr_Code'] matches df2['Curr_Code'].

Code:

##some other code
df1 = old_df[req_cols]

cnt = len(df1.index)
df1['Conv_Amount'] = df1.merge(df2).assign(soln=lambda df: df.Amount/ df.Conv_Value).soln
tot_amt = df1['Conv_Amount'].sum()

After merge/divide df1['Conv_Amount'] is not having the values im expecting and im seeing this warning:

SettingWithCopyWarning:
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  df1['Conv_Amount'] = df1.merge(df2).assign(soln=lambda df: df.Amount/ df.Conv_Value).soln

The same code was working well before but not now. I have tried many solutions from SO but no luck. Im a newbie to pandas and trying to understand these indexing concepts. Any help is really appreciated. Thanks!

asked Jun 17 '21 at 10:50

Mr.B

Use `df1 = old_df[req_cols].copy()` – jezrael Jun 17 '21 at 10:51
@jezrael warning is gone now, thanks. But im having some discrepancies whats there in df1['Conv_Amount'] column. Could you pls help me out on this? – Mr.B Jun 17 '21 at 10:55
without data hard to know problem. – jezrael Jun 17 '21 at 10:55
Data is huge, let me try to add some sample data – Mr.B Jun 17 '21 at 10:59
Also pls tell, is it mandatory to sort both df's on a column column before merging. – Mr.B Jun 17 '21 at 11:04

How to solve SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame

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