def get_assignment(self, selections=None):
        if selections is None or len(list(selections.keys())) == 0:
            dims = [dim for dim in self.dims if dim not in self.attrs]
            return {dim: sel for dim, sel in
                    zip(dims, self._df.columns.tolist())}
        else:
            return selections
Get a mapping between dimension and selection when none are provided.
dataset/ETHPy150Open bokeh/bokeh/bokeh/charts/data_source.py/OrderedAssigner.get_assignment