Replacing values in multiple specific columns of a Dataframe
You cannnot use inplace=True, because subset returns a Series which may have its data as a view. Modifying it in place doesn't ALWAYS propogate it back to the parent object. That's why SettingWithCopyWarning is possible there (or raise if you set the option). You should never do this, nor is their ever a reason to do so.
df[['Score2', 'Score3']] = df[['Score2', 'Score3']].replace(-999, np.nan)print (df) Score1 Score2 Score30 42 NaN 2.01 52 NaN 2.02 -999 NaN NaN3 24 2.0 2.04 73 1.0 NaN