Weight unique values: returns a dataframe with a count
        of unique values

def wunique_(self, col):
        """
        Weight unique values: returns a dataframe with a count
        of unique values
        """
        try:
            s = pd.value_counts(self.df[col].values)
            df = pd.DataFrame(s, columns=["Number"])
            return df
        except Exception as e:
            self.err(e, "Can not weight unique data")