optimized combine_indices function by using numpy's intersect1d for better performance

mvcm/utility_functions.py

@@ -131,15 +131,15 @@ def restoral_flag(bits: np.ndarray) -> np.ndarray:
     return np.logical_not(np.logical_and(qa_bit, np.logical_not(test_bit)))
 
 
+# attempt at optimizing combine_indices
 def combine_indices(index1: tuple, index2: tuple, shape: tuple) -> tuple:
     """Combine two sets of indices and returns their intersection."""
-    idx1 = list(np.ravel_multi_index(index1, shape))
-    idx2 = list(np.ravel_multi_index(index2, shape))
+    idx1 = np.ravel_multi_index(index1, shape)
+    idx2 = np.ravel_multi_index(index2, shape)
 
-    intersect_idx = list(set(idx1).intersection(set(idx2)))
-
-    return tuple(np.unravel_index(np.array(intersect_idx, dtype=np.intp), shape))
+    intersect_idx = np.intersect1d(idx1, idx2)
 
+    return tuple(np.unravel_index(intersect_idx, shape))
 
 def set_cm_bytes(cloud_mask: np.ndarray, bits: dict, pixel_type: xr.Dataset) -> np.ndarray:
     """Compute cloud mask bytes."""