ENH: add public methods Dataset.get_host_cell_index and Dataset.is_so…

…rted

src/gpgi/types.py

@@ -481,6 +481,30 @@ def _setup_host_cell_index(self, verbose: bool = False) -> None:
                 f"Indexed {self.particles.count:.4g} particles in {(tstop-tstart)/1e9:.2f} s"
             )
 
+    def get_host_cell_index(self) -> np.ndarray[Any, np.dtype("uint16")]:
+        r"""
+        Return a copy of the host cell index (HCI), representing the ndimensional index
+        of the host cell for each particle.
+        The return array has shape (particles.count, grid.ndim).
+        """
+        self._setup_host_cell_index()
+        return self._hci.copy()
+
+    def is_sorted(self) -> bool:
+        r"""
+        Return True if particles memory layout matches the spatial distribution, False
+        otherwise.
+        """
+        self._setup_host_cell_index()
+        hci = self._hci
+        if self.grid.ndim == 1:
+            ind = np.lexsort((hci[:, 0],))
+        elif self.grid.ndim == 2:
+            ind = np.lexsort((hci[:, 0], hci[:, 1]))
+        else:
+            ind = np.lexsort((hci[:, 0], hci[:, 1], hci[:, 2]))
+        return np.all(hci == hci[ind])
+
     def deposit(
         self,
         particle_field_key: Name,