1586 Add greater_or_equal option to Checkpoint handler

ignite/handlers/checkpoint.py

@@ -98,6 +98,8 @@ class Checkpoint(Serializable):
             details.
         include_self (bool): Whether to include the `state_dict` of this object in the checkpoint. If `True`, then
             there must not be another object in ``to_save`` with key ``checkpointer``.
+        greater_or_equal (bool): if `True`, the latest equally scored model is stored. Otherwise, the first model.
+            Default, `False`.
 
     .. _DistributedDataParallel: https://pytorch.org/docs/stable/generated/
         torch.nn.parallel.DistributedDataParallel.html
@@ -261,6 +263,7 @@ def __init__(
         global_step_transform: Optional[Callable] = None,
         filename_pattern: Optional[str] = None,
         include_self: bool = False,
+        greater_or_equal: bool = False,
     ) -> None:
 
         if to_save is not None:  # for compatibility with ModelCheckpoint
@@ -301,6 +304,7 @@ def __init__(
         self.filename_pattern = filename_pattern
         self._saved = []  # type: List["Checkpoint.Item"]
         self.include_self = include_self
+        self.greater_or_equal = greater_or_equal
 
     def reset(self) -> None:
         """Method to reset saved checkpoint names.
@@ -339,6 +343,12 @@ def _check_lt_n_saved(self, or_equal: bool = False) -> bool:
             return True
         return len(self._saved) < self.n_saved + int(or_equal)
 
+    def _compare_fn(self, new: Union[int, float]) -> bool:
+        if self.greater_or_equal:
+            return new >= self._saved[0].priority
+        else:
+            return new > self._saved[0].priority
+
     def __call__(self, engine: Engine) -> None:
 
         global_step = None
@@ -354,7 +364,7 @@ def __call__(self, engine: Engine) -> None:
                 global_step = engine.state.get_event_attrib_value(Events.ITERATION_COMPLETED)
             priority = global_step
 
-        if self._check_lt_n_saved() or self._saved[0].priority < priority:
+        if self._check_lt_n_saved() or self._compare_fn(priority):
 
             priority_str = f"{priority}" if isinstance(priority, numbers.Integral) else f"{priority:.4f}"
 

tests/ignite/handlers/test_checkpoint.py

@@ -1526,3 +1526,36 @@ def test_checkpoint_reset_with_engine(dirname):
     expected += [f"{_PREFIX}_{name}_{i}.pt" for i in [1 * 2, 2 * 2]]
     assert sorted(os.listdir(dirname)) == sorted(expected)
     assert "PREFIX_model_4.pt" in handler.last_checkpoint
+
+
+def test_greater_or_equal():
+    scores = iter([1, 2, 2, 2])
+
+    def score_function(_):
+        return next(scores)
+
+    class Saver:
+        def __init__(self):
+            self.counter = 0
+
+        def __call__(self, c, f, m):
+            if self.counter == 0:
+                assert f == "model_1.pt"
+            else:
+                assert f == "model_2.pt"
+            self.counter += 1
+
+    handler = Saver()
+
+    checkpointer = Checkpoint(
+        to_save={"model": DummyModel()},
+        save_handler=handler,
+        score_function=score_function,
+        n_saved=2,
+        greater_or_equal=True,
+    )
+    trainer = Engine(lambda e, b: None)
+
+    for _ in range(4):
+        checkpointer(trainer)
+    assert handler.counter == 4