Faster Accuracy metric (#2775)

* Faster classfication stats

* Faster accuracy metric

* minor change on cls metric

* Add out-of-bound class clamping

* Add more tests and minor fixes

* Resolve code style warning

* Update for #2781

* hotfix

* Update pytorch_lightning/metrics/functional/classification.py

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

* Update about conversation

* Add docstring on stat_scores_multiple_classes

Co-authored-by: Younghun Roh <yhunroh@mindslab.ai>
Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

pytorch_lightning/metrics/functional/classification.py

@@ -138,10 +138,10 @@ def stat_scores_multiple_classes(
         target: torch.Tensor,
         num_classes: Optional[int] = None,
         argmax_dim: int = 1,
+        reduction: str = 'none',
 ) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor, torch.Tensor, torch.Tensor]:
     """
-    Calls the stat_scores function iteratively for all classes, thus
-    calculating the number of true postive, false postive, true negative
+    Calculates the number of true postive, false postive, true negative
     and false negative for each class
 
     Args:
@@ -150,6 +150,12 @@ def stat_scores_multiple_classes(
         num_classes: number of classes if known
         argmax_dim: if pred is a tensor of probabilities, this indicates the
             axis the argmax transformation will be applied over
+        reduction: method for reducing result values (default: none)
+            Available reduction methods:
+
+            - elementwise_mean: takes the mean
+            - none: pass array
+            - sum: add elements
 
     Return:
         True Positive, False Positive, True Negative, False Negative, Support
@@ -173,16 +179,58 @@ def stat_scores_multiple_classes(
     if pred.ndim == target.ndim + 1:
         pred = to_categorical(pred, argmax_dim=argmax_dim)
 
-    num_classes = get_num_classes(pred=pred, target=target,
-                                  num_classes=num_classes)
+    num_classes = get_num_classes(pred=pred, target=target, num_classes=num_classes)
 
-    tps = torch.zeros((num_classes,), device=pred.device)
-    fps = torch.zeros((num_classes,), device=pred.device)
-    tns = torch.zeros((num_classes,), device=pred.device)
-    fns = torch.zeros((num_classes,), device=pred.device)
-    sups = torch.zeros((num_classes,), device=pred.device)
-    for c in range(num_classes):
-        tps[c], fps[c], tns[c], fns[c], sups[c] = stat_scores(pred=pred, target=target, class_index=c)
+    if pred.dtype != torch.bool:
+        pred.clamp_max_(max=num_classes)
+    if target.dtype != torch.bool:
+        target.clamp_max_(max=num_classes)
+
+    possible_reductions = ('none', 'sum', 'elementwise_mean')
+    if reduction not in possible_reductions:
+        raise ValueError("reduction type %s not supported" % reduction)
+
+    if reduction == 'none':
+        pred = pred.view((-1, )).long()
+        target = target.view((-1, )).long()
+
+        tps = torch.zeros((num_classes + 1,), device=pred.device)
+        fps = torch.zeros((num_classes + 1,), device=pred.device)
+        tns = torch.zeros((num_classes + 1,), device=pred.device)
+        fns = torch.zeros((num_classes + 1,), device=pred.device)
+        sups = torch.zeros((num_classes + 1,), device=pred.device)
+
+        match_true = (pred == target).float()
+        match_false = 1 - match_true
+
+        tps.scatter_add_(0, pred, match_true)
+        fps.scatter_add_(0, pred, match_false)
+        fns.scatter_add_(0, target, match_false)
+        tns = pred.size(0) - (tps + fps + fns)
+        sups.scatter_add_(0, target, torch.ones_like(match_true))
+
+        tps = tps[:num_classes]
+        fps = fps[:num_classes]
+        tns = tns[:num_classes]
+        fns = fns[:num_classes]
+        sups = sups[:num_classes]
+
+    elif reduction == 'sum' or reduction == 'elementwise_mean':
+        count_match_true = (pred == target).sum().float()
+        oob_tp, oob_fp, oob_tn, oob_fn, oob_sup = stat_scores(pred, target, num_classes, argmax_dim)
+
+        tps = count_match_true - oob_tp
+        fps = pred.nelement() - count_match_true - oob_fp
+        fns = pred.nelement() - count_match_true - oob_fn
+        tns = pred.nelement() * (num_classes + 1) - (tps + fps + fns + oob_tn)
+        sups = pred.nelement() - oob_sup.float()
+
+        if reduction == 'elementwise_mean':
+            tps /= num_classes
+            fps /= num_classes
+            fns /= num_classes
+            tns /= num_classes
+            sups /= num_classes
 
     return tps, fps, tns, fns, sups
 
@@ -218,16 +266,13 @@ def accuracy(
         tensor(0.7500)
 
     """
-    tps, fps, tns, fns, sups = stat_scores_multiple_classes(
-        pred=pred, target=target, num_classes=num_classes)
-
     if not (target > 0).any() and num_classes is None:
         raise RuntimeError("cannot infer num_classes when target is all zero")
 
-    if reduction in ('elementwise_mean', 'sum'):
-        return reduce(sum(tps) / sum(sups), reduction=reduction)
-    if reduction == 'none':
-        return reduce(tps / sups, reduction=reduction)
+    tps, fps, tns, fns, sups = stat_scores_multiple_classes(
+        pred=pred, target=target, num_classes=num_classes, reduction=reduction)
+
+    return tps / sups
 
 
 def confusion_matrix(

tests/metrics/functional/test_classification.py

@@ -121,15 +121,19 @@ def test_stat_scores(pred, target, expected_tp, expected_fp, expected_tn, expect
     assert sup.item() == expected_support
 
 
-@pytest.mark.parametrize(['pred', 'target', 'expected_tp', 'expected_fp',
+@pytest.mark.parametrize(['pred', 'target', 'reduction', 'expected_tp', 'expected_fp',
                           'expected_tn', 'expected_fn', 'expected_support'], [
-    pytest.param(torch.tensor([0., 2., 4., 4.]), torch.tensor([0., 4., 3., 4.]),
+    pytest.param(torch.tensor([0., 2., 4., 4.]), torch.tensor([0., 4., 3., 4.]), 'none',
+                 [1, 0, 0, 0, 1], [0, 0, 1, 0, 1], [3, 4, 3, 3, 1], [0, 0, 0, 1, 1], [1, 0, 0, 1, 2]),
+    pytest.param(to_onehot(torch.tensor([0., 2., 4., 4.])), torch.tensor([0., 4., 3., 4.]), 'none',
                  [1, 0, 0, 0, 1], [0, 0, 1, 0, 1], [3, 4, 3, 3, 1], [0, 0, 0, 1, 1], [1, 0, 0, 1, 2]),
-    pytest.param(to_onehot(torch.tensor([0., 2., 4., 4.])), torch.tensor([0., 4., 3., 4.]),
-                 [1, 0, 0, 0, 1], [0, 0, 1, 0, 1], [3, 4, 3, 3, 1], [0, 0, 0, 1, 1], [1, 0, 0, 1, 2])
+    pytest.param(to_onehot(torch.tensor([0., 2., 4., 4.])), torch.tensor([0., 4., 3., 4.]), 'sum',
+                 torch.tensor(2), torch.tensor(2), torch.tensor(14), torch.tensor(2), torch.tensor(4)),
+    pytest.param(to_onehot(torch.tensor([0., 2., 4., 4.])), torch.tensor([0., 4., 3., 4.]), 'elementwise_mean',
+                 torch.tensor(0.4), torch.tensor(0.4), torch.tensor(2.8), torch.tensor(0.4), torch.tensor(0.8))
 ])
-def test_stat_scores_multiclass(pred, target, expected_tp, expected_fp, expected_tn, expected_fn, expected_support):
-    tp, fp, tn, fn, sup = stat_scores_multiple_classes(pred, target)
+def test_stat_scores_multiclass(pred, target, reduction, expected_tp, expected_fp, expected_tn, expected_fn, expected_support):
+    tp, fp, tn, fn, sup = stat_scores_multiple_classes(pred, target, reduction=reduction)
 
     assert torch.allclose(torch.tensor(expected_tp).to(tp), tp)
     assert torch.allclose(torch.tensor(expected_fp).to(fp), fp)