def difflag1(self):
        """
        Conduct a diff-1 transform on a numeric frame column.

        :returns: an H2OFrame where each element is equal to the corresponding element in the source
            frame minus the previous-row element in the same frame.
        """
        if self.ncols > 1:
            raise H2OValueError("Only single-column frames supported")
        if self.types[self.columns[0]] not in {"real", "int", "bool"}:
            raise H2OValueError("Numeric column expected")
        fr = H2OFrame._expr(expr=ExprNode("difflag1", self), cache=self._ex._cache)
        return fr
Conduct a diff-1 transform on a numeric frame column.

        :returns: an H2OFrame where each element is equal to the corresponding element in the source
            frame minus the previous-row element in the same frame.