[Bugfix] Fix 5873 (#5884)

Co-authored-by: Hongzhi (Steve), Chen <chenhongzhi.nkcs@gmail.com>

python/dgl/heterograph.py

@@ -5263,12 +5263,12 @@ class DGLGraph(object):
             out = reduce_dict_data(frames, cross_reducer, merge_order[dtid])
             # Replace infinity with zero for isolated nodes when reducer is min/max
             if core.is_builtin(rfunc) and rfunc.name in ["min", "max"]:
-                key = list(out.keys())[0]
-                out[key] = (
-                    F.replace_inf_with_zero(out[key])
-                    if out[key] is not None
-                    else None
-                )
+                for key in out.keys():
+                    out[key] = (
+                        F.replace_inf_with_zero(out[key])
+                        if out[key] is not None
+                        else None
+                    )
             self._node_frames[dtid].update(out)
             # apply
             if apply_node_func is not None:

tests/python/common/test_heterograph-update-all.py

@@ -334,6 +334,38 @@ def test_binary_op(idtype):
                 _test(lhs, rhs, binary_op, reducer)
 
 
+# Issue #5873
+def test_multi_update_all_minmax_reduce_with_isolated_nodes():
+    g = dgl.heterograph(
+        {
+            ("A", "AB", "B"): ([0, 1, 2, 3], [0, 0, 1, 1]),
+            ("C", "CB", "B"): ([0, 1, 2, 3], [2, 2, 3, 3]),
+        },
+        device=F.ctx(),
+    )
+    g.nodes["A"].data["x"] = F.randn((4, 16))
+    g.nodes["C"].data["x"] = F.randn((4, 16))
+    g.multi_update_all(
+        {
+            "AB": (dgl.function.copy_u("x", "m"), dgl.function.min("m", "a1")),
+            "CB": (dgl.function.copy_u("x", "m"), dgl.function.min("m", "a2")),
+        },
+        cross_reducer="min",
+    )
+    assert not np.isinf(F.asnumpy(g.nodes["B"].data["a1"])).any()
+    assert not np.isinf(F.asnumpy(g.nodes["B"].data["a2"])).any()
+
+    g.multi_update_all(
+        {
+            "AB": (dgl.function.copy_u("x", "m"), dgl.function.max("m", "a1")),
+            "CB": (dgl.function.copy_u("x", "m"), dgl.function.max("m", "a2")),
+        },
+        cross_reducer="max",
+    )
+    assert not np.isinf(F.asnumpy(g.nodes["B"].data["a1"])).any()
+    assert not np.isinf(F.asnumpy(g.nodes["B"].data["a2"])).any()
+
+
 if __name__ == "__main__":
     test_unary_copy_u()
     test_unary_copy_e()