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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 index_by(self, column_or_label):
 """Return a dict keyed by values in a column that contains lists of rows corresponding to each value. """

        column = self._get_column(column_or_label)
        index = {}
        for key, row in zip(column, self.rows):
            index.setdefault(key, []).append(row)
        return index