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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 to_json(self):
 """Convert Data Collection to a dictionary."""

        return {
            'header': self.header.to_json(),
            'values': self._values,
            'datetimes': self.datetimes,
            'validated_a_period': self._validated_a_period
        }