Writes component numbers to a table.

def write_how_many(self, file):
        """ Writes component numbers to a table.
        """
        report = CaseReport(self.case)

        # Map component labels to attribute names
        components = [("Bus", "n_buses"), ("Generator", "n_generators"),
            ("Committed Generator", "n_online_generators"),
            ("Load", "n_loads"), ("Fixed Load", "n_fixed_loads"),
            ("Despatchable Load", "n_online_vloads"), ("Shunt", "n_shunts"),
            ("Branch", "n_branches"), ("Transformer", "n_transformers"),
            ("Inter-tie", "n_interties"), ("Area", "n_areas")
        ]

        # Column 1 width
        longest = max([len(c[0]) for c in components])

        col1_header = "Object"
        col1_width = longest
        col2_header = "Quantity"
        col2_width = len(col2_header)

        # Row separator
        sep = "="*col1_width + " " + "="*col2_width + "\n"

        # Row headers
        file.write(sep)

        file.write(col1_header.center(col1_width))
        file.write(" ")
        file.write("%s\n" % col2_header.center(col2_width))

        file.write(sep)

        # Rows
        for label, attr in components:
            col2_value = str(getattr(report, attr))
            file.write("%s %s\n" %
                (label.ljust(col1_width), col2_value.rjust(col2_width)))
        else:
            file.write(sep)
            file.write("\n")

        del report