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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def normalize(self):
 """ Normalize data. """


        if self.preprocessed_data.empty:
            data = self.original_data
        else:
            data = self.preprocessed_data

        data = pd.DataFrame(preprocessing.normalize(data), columns=data.columns, index=data.index)
        self.preprocessed_data = data