Add Metric.from_mask helper method (facebookresearch#3411)

Author: poojasethi

parlai/core/metrics.py

@@ -24,6 +24,7 @@
     Optional,
     Set,
     Tuple,
+    Type,
     Union,
 )
 
@@ -272,7 +273,7 @@ def many(cls, *objs: List[TVector]) -> List[Metric]:
         """
         Construct many of a Metric from the base parts.
 
-        Useful if you separately compute numerators and denomenators, etc.
+        Useful if you separately compute numerators and denominators, etc.
         """
         lengths = [len(o) for o in objs]
         objs = list(objs)  # convert from tuple for inplace modification
@@ -286,6 +287,27 @@ def many(cls, *objs: List[TVector]) -> List[Metric]:
             raise IndexError(f'Uneven {cls.__name__} constructions: {lengths}')
         return [cls(*items) for items in zip(*objs)]
 
+    @classmethod
+    def from_mask(
+        cls, metric_per_token: torch.Tensor, mask: torch.Tensor, MyMetric: Type[Metric]
+    ) -> List[Metric]:
+        """
+        From token-level metrics, returns an aggregate MyMetric per example in the batch.
+
+        :param metric_per_token:
+            a (batchsize x num_tokens) Tensor
+        :param mask:
+            a (batchsize x num_tokens) Tensor to mask out tokens that should *not* be considered in the aggregate metric calculation.
+        :param MyMetric:
+            a subclass of Metric
+        :return:
+            a (batchsize) Tensor
+        """
+        tokens_per_ex = mask.long().sum(dim=-1)
+        metric_per_ex = (metric_per_token * mask).sum(dim=-1)
+        metrics = MyMetric.many(metric_per_ex, tokens_per_ex)
+        return metrics
+
 
 class FixedMetric(Metric):
     """

parlai/core/torch_generator_agent.py

@@ -34,7 +34,7 @@
 from parlai.utils.misc import warn_once
 from parlai.utils.io import PathManager
 import parlai.utils.logging as logging
-from parlai.core.metrics import SumMetric, AverageMetric, FairseqBleuMetric
+from parlai.core.metrics import Metric, SumMetric, AverageMetric, FairseqBleuMetric
 from parlai.utils.fp16 import FP16SafeCrossEntropy
 import parlai.utils.fsdp as fsdp_utils
 from parlai.utils.torch import (
@@ -710,28 +710,35 @@ def compute_loss(self, batch, return_output=False):
         model_output = self.model(*self._model_input(batch), ys=batch.label_vec)
         scores, preds, *_ = model_output
         score_view = scores.reshape(-1, scores.size(-1))
-        loss = self.criterion(score_view, batch.label_vec.view(-1))
-        loss = loss.view(scores.shape[:-1]).sum(dim=1)
-        # save loss to metrics
+        loss_flattened = self.criterion(score_view, batch.label_vec.view(-1))
+        loss_per_token = loss_flattened.view(scores.shape[:-1])
         notnull = batch.label_vec.ne(self.NULL_IDX)
-        target_tokens = notnull.long().sum(dim=-1)
-        correct = ((batch.label_vec == preds) * notnull).sum(dim=-1)
 
+        # save loss to metrics
         # cross entropy loss
-        self.record_local_metric('loss', AverageMetric.many(loss, target_tokens))
+        self.record_local_metric(
+            'loss', Metric.from_mask(loss_per_token, notnull, AverageMetric)
+        )
         # perplexity
-        self.record_local_metric('ppl', PPLMetric.many(loss, target_tokens))
+        self.record_local_metric(
+            'ppl', Metric.from_mask(loss_per_token, notnull, PPLMetric)
+        )
         # token-wise accuracy
         self.record_local_metric(
-            'token_acc', AverageMetric.many(correct, target_tokens)
+            'token_acc',
+            Metric.from_mask(batch.label_vec == preds, notnull, AverageMetric),
         )
         # utterance-wise exact match
+        num_target_tokens = notnull.long().sum(dim=-1)
+        num_tokens_correct = ((batch.label_vec == preds) * notnull).sum(dim=-1)
         self.record_local_metric(
-            'token_em', AverageMetric.many(correct == target_tokens)
+            'token_em', AverageMetric.many(num_tokens_correct == num_target_tokens)
         )
+
         # actually do backwards loss
+        loss = loss_per_token.sum(dim=1)
         loss = loss.sum()
-        loss /= target_tokens.sum()  # average loss per token
+        loss /= num_target_tokens.sum()  # average loss per token
         if return_output:
             return (loss, model_output)
         else:
@@ -1440,7 +1447,7 @@ def set_block_list(self: TSType, block_list: Optional[SearchBlocklist]) -> TSTyp
 
     def get_output_from_current_step(self):
         """
-        Get the outputput at the current step.
+        Get the output at the current step.
         """
         return self.outputs[-1]
 

tests/test_metrics.py

@@ -13,6 +13,7 @@
     AverageMetric,
     SumMetric,
     FixedMetric,
+    Metric,
     Metrics,
     GlobalAverageMetric,
     MacroAverageMetric,
@@ -28,6 +29,7 @@
     WeightedF1Metric,
     AUCMetrics,
 )
+from parlai.core.torch_generator_agent import PPLMetric
 import parlai.utils.testing as testing_utils
 
 
@@ -70,7 +72,6 @@ def test_sum_metric_additions(self):
             self.assertAlmostEqual(actual_output, output, places=6)
 
     def test_average_metric_inputs(self):
-
         passing_inputs_and_outputs = [
             ((2, 4), 0.5),
             ((17.0, 10.0), 1.7),
@@ -91,7 +92,6 @@ def test_average_metric_inputs(self):
                 AverageMetric(input_[0], input_[1])
 
     def test_average_metric_additions(self):
-
         input_pairs_and_outputs = [
             ((2, 4), (1.5, 1), 0.7),
             (
@@ -120,6 +120,96 @@ def test_macroaverage_additions(self):
         assert (m1 + m2) == AverageMetric(4, 7)
         assert MacroAverageMetric({'a': m1, 'b': m2}) == 0.5 * (1.0 / 3 + 3.0 / 4)
 
+    def test_average_metric_from_mask(self) -> None:
+        # first test case. batchsize=3, num_tokens=10
+        token_values_1 = torch.FloatTensor(
+            [
+                [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+                [-10, -8, -6, -4, -2, 0, 2, 4, 6, 8],
+                [0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0],
+            ]
+        )
+        token_mask_1 = torch.LongTensor(
+            [
+                [1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
+                [1, 1, 1, 1, 1, 1, 0, 0, 0, 0],
+                [1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
+            ]
+        )
+        output_1 = [
+            AverageMetric(55, 10),
+            AverageMetric(-30, 6),
+            AverageMetric(12.5, 5),
+        ]
+
+        # second test case. batchsize=4, num_tokens=5
+        token_values_2 = torch.FloatTensor(
+            [
+                [1, 2, 3, 4, 5],
+                [1.5, 0, -1, 3, -4],
+                [-3, -2, -1, 0, 1],
+                [4, 5, 6, 7, 8],
+            ]
+        )
+        token_mask_2 = torch.LongTensor(
+            [
+                [1, 1, 1, 1, 1],
+                [1, 1, 1, 0, 0],
+                [1, 0, 1, 0, 1],
+                [0, 0, 0, 0, 0],
+            ]
+        )
+        output_2 = [
+            AverageMetric(15, 5),
+            AverageMetric(0.5, 3),
+            AverageMetric(-3, 3),
+            AverageMetric(0, 0),
+        ]
+
+        input_and_outputs = [
+            (token_values_1, token_mask_1, output_1),
+            (token_values_2, token_mask_2, output_2),
+        ]
+
+        for token_values, token_mask, output in input_and_outputs:
+            actual_output = Metric.from_mask(token_values, token_mask, AverageMetric)
+            self.assertEqual(len(actual_output), len(output))
+            # Because Metric.from_mask() calls Metric.many(), which in turn converts tensors to lists,
+            # it possible for the actual and expected outputs to be close to each other but not exactly equal.
+            for a, o in zip(actual_output, output):
+                self.assertIsInstance(a, type(o))
+                self.assertAlmostEqual(a.value(), o.value(), places=6)
+
+    def test_ppl_metric_from_mask(self) -> None:
+        # batchsize=3, num_tokens=10
+        token_values = torch.FloatTensor(
+            [
+                [0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9],
+                [0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1],
+                [0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1],
+            ]
+        )
+        token_mask = torch.LongTensor(
+            [
+                [1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
+                [1, 1, 1, 1, 1, 1, 0, 0, 0, 0],
+                [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+            ]
+        )
+        output = [
+            PPLMetric(4.5, 10),
+            PPLMetric(0.6, 6),
+            PPLMetric(0, 0),
+        ]
+        actual_output = Metric.from_mask(token_values, token_mask, PPLMetric)
+
+        self.assertEqual(len(actual_output), len(output))
+        # Because Metric.from_mask() calls Metric.many(), which in turn converts tensors to lists,
+        # it possible for the actual and expected outputs to be close to each other but not exactly equal.
+        for a, o in zip(actual_output, output):
+            self.assertIsInstance(a, type(o))
+            self.assertAlmostEqual(a.value(), o.value(), places=6)
+
 
 class TestMetrics(unittest.TestCase):
     """