facet_wrap.py 文件源码

def map(self, data, layout):
        if not len(data):
            data['PANEL'] = pd.Categorical(
                [],
                categories=layout['PANEL'].cat.categories,
                ordered=True)
            return data

        facet_vals = eval_facet_vars(data, self.vars, self.plot.environment)
        data, facet_vals = add_missing_facets(data, layout,
                                              self.vars, facet_vals)

        # assign each point to a panel
        keys = join_keys(facet_vals, layout, self.vars)
        data['PANEL'] = match(keys['x'], keys['y'], start=1)
        data = data.sort_values('PANEL', kind='mergesort')

        # matching dtype
        data['PANEL'] = pd.Categorical(
            data['PANEL'],
            categories=layout['PANEL'].cat.categories,
            ordered=True)

        data.reset_index(drop=True, inplace=True)
        return data