Why I get an error while working on a slice of dataframe?

Question

I have a filtered dataframe called df_final, I wanted two have additional tabs. For tab 2, I create a new column, then do filterig on that column and save it, then delete the created column and save it as tab 1. Here is the code:

  df_final = df.query(query)
  df_final["Duplicate"] = df_final.duplicated(subset=['DR/ER#'])
  df_tab2 = df_final.loc[df_final['Duplicate']== True]
  df_tab1 = df_final.drop(columns = ['Duplicate', 'DR/ER#'])
  df_tab1.to_excel(writer, sheet_name = 'DR ER')
  df_tab2.to_excel(writer, sheet_name = 'DR ER duplicates')

but I get this Error.

<ipython-input-6-4e0fc04c4f3a>:46: 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
  df_final["Duplicate"] = df_final.duplicated(subset=['DR/ER#'])

Please, help me.

Did you See the caveats in the documentation:... as the message suggested? Try searching SO with the error message, you should get plenty of information. — wwii
– wwii, Commented Jul 15, 2021 at 17:05
Did you try using the method suggested in the error message? - Try using .loc[row_indexer,col_indexer] = value instead — wwii
– wwii, Commented Jul 15, 2021 at 17:09
I didn;t get the method, for which I need to do that? I searched the method but didn't get anything on how it works — Anna Abrahamyan
– Anna Abrahamyan, Commented Jul 15, 2021 at 17:20

Valdi_Bo · Accepted Answer · 2021-07-15 17:59:57Z

1

df_final is actually a view of the original DataFrame (sharing its data buffer), so you cannot alter it.

If you want to alter df_final, create it as a new DataFrame (with its own data buffer). To do it, run e.g.:

df_final = df.query(query).copy()

and the "link" to the original DataFrame will no longer exist.

answered Jul 15, 2021 at 17:59

Valdi_Bo

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