def startswith(self, prefix):
        """
        Construct a Filter matching values starting with ``prefix``.

        Parameters
        ----------
        prefix : str
            String prefix against which to compare values produced by ``self``.

        Returns
        -------
        matches : Filter
            Filter returning True for all sid/date pairs for which ``self``
            produces a string starting with ``prefix``.
        """
        return ArrayPredicate(
            term=self,
            op=LabelArray.startswith,
            opargs=(prefix,),
        )