df.loc causes a SettingWithCopyWarning warning message

Question

The following line of my code causes a warning :

import pandas as pd

s = pd.DataFrame(np.random.randint(0,100,size=(100, 4)), columns=list(\'ABCD\'))
s.loc[         


        

Answer 1

The documentation is slightly confusing.

Your dataframe is a copy of another dataframe. You can verify this by running bool(df.is_copy) You are getting the warning because you are trying to assign to this copy.

The warning/documentation is telling you how you should have constructed df in the first place. Not how you should assign to it now that it is a copy.

df = some_other_df[cols]

will make df a copy of some_other_df. The warning suggests doing this instead

df = some_other_df.loc[:, [cols]]

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Now that it is done, if you choose to ignore this warning, you could

df = df.copy()

or

df.is_copy = None