DataFrame fillna mit 0
df['column'] = df['column'].fillna(0)
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df['column'] = df['column'].fillna(0)sub2['income'].fillna((sub2['income'].mean()), inplace=True)df.fillna(np.nan).replace([np.nan], [None])df.fillna(np.nan).replace([np.nan], [None])# selecting your desired columns
df[['a', 'b']] = df[['a', 'b']].fillna(df['c'], inplace=True)When inplace = True , the data is modified in place, which means it will return nothing and the dataframe is now updated. When inplace = False , which is the default, then the operation is performed and it returns a copy of the object. You then need to save it to something.