tweak(merge): fix warnings and minor speedups

src/agora/utils/merge.py

@@ -41,13 +41,15 @@ def apply_merges(data: pd.DataFrame, merges: np.ndarray):
     # Implement the merges and drop source rows.
     if valid_merges.any():
         to_merge = data.loc[indices]
-        for target, source in merges[valid_merges]:
-            target, source = tuple(target), tuple(source)
-            to_merge.loc[target] = join_tracks_pair(
-                to_merge.loc[target].values,
-                to_merge.loc[source].values,
+        targets, sources = zip(*merges[valid_merges])
+        for source, target in zip(sources, targets):
+            to_merge.loc[target] = copy(
+                join_tracks_pair(
+                    to_merge.loc[tuple(target)].values,
+                    to_merge.loc[tuple(source)].values,
+                )
             )
-            to_merge.drop(source, inplace=True)
+        to_merge.drop(map(tuple, sources), inplace=True)
 
         merged = pd.concat((merged, to_merge), names=data.index.names)
     return merged
@@ -57,7 +59,7 @@ def join_tracks_pair(target: np.ndarray, source: np.ndarray) -> np.ndarray:
     """
     Join two tracks and return the new value of the target.
     """
-    target_copy = copy(target)
+    target_copy = target
     end = find_1st(target_copy[::-1], 0, cmp_larger)
     target_copy[-end:] = source[-end:]
     return target_copy