def labels_and_ticks(self):
        """Collect labels and ticks from plotters."""
        labels, idxs = [], []
        for plotter in self.plotters.values():
            sub_labels, sub_idxs, _, _ = plotter.labels_ticks_and_vals()
            labels.append(sub_labels)
            idxs.append(sub_idxs)
        return np.concatenate(labels), np.concatenate(idxs)
Collect labels and ticks from plotters.