added shuffle disable option in BucketBatchSampler

CHANGELOG.md

@@ -30,6 +30,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `SpanExtractorWithSpanWidthEmbedding`, putting specific span embedding computations into the `_embed_spans` method and leaving the common code in `SpanExtractorWithSpanWidthEmbedding` to unify the arguments, and modified `BidirectionalEndpointSpanExtractor`, `EndpointSpanExtractor` and `SelfAttentiveSpanExtractor` accordingly. Now, `SelfAttentiveSpanExtractor` can also embed span widths.
 - Added a `min_steps` parameter to `BeamSearch` to set a minimum length for the predicted sequences.
 - Added the `FinalSequenceScorer` abstraction to calculate the final scores of the generated sequences in `BeamSearch`. 
+- Added `shuffle` argument to `BucketBatchSampler` which allows for disabling shuffling.
 
 ### Fixed
 

allennlp/data/samplers/bucket_batch_sampler.py

@@ -57,6 +57,10 @@ class BucketBatchSampler(BatchSampler):
         If `True`, the sampler will drop the last batch if
         its size would be less than batch_size`.
 
+    shuffle : `bool`, (default = `True`)
+        If `False`, the sampler won't shuffle the batches. `padding_noise` will be ignored and set
+        to `0.0`.
+
     """
 
     def __init__(
@@ -65,11 +69,15 @@ def __init__(
         sorting_keys: List[str] = None,
         padding_noise: float = 0.1,
         drop_last: bool = False,
+        shuffle: bool = True,
     ):
         self.sorting_keys = sorting_keys
         self.padding_noise = padding_noise
         self.batch_size = batch_size
         self.drop_last = drop_last
+        self.shuffle = shuffle
+        if not shuffle:
+            self.padding_noise = 0.0
 
     def _argsort_by_padding(
         self, instances: Iterable[Instance]
@@ -113,7 +121,8 @@ def get_batch_indices(self, instances: Sequence[Instance]) -> Iterable[List[int]
             if self.drop_last and len(batch_indices) < self.batch_size:
                 continue
             batches.append(batch_indices)
-        random.shuffle(batches)
+        if self.shuffle:
+            random.shuffle(batches)
         for batch in batches:
             yield batch
 

tests/data/samplers/bucket_batch_sampler_test.py

@@ -24,6 +24,20 @@ def test_create_batches_groups_correctly(self):
             expected_groups.remove(group)
         assert expected_groups == []
 
+    def test_disable_shuffle(self):
+        sampler = BucketBatchSampler(batch_size=2, sorting_keys=["text"], shuffle=False)
+
+        grouped_instances = []
+        for indices in sampler.get_batch_indices(self.instances):
+            grouped_instances.append([self.instances[idx] for idx in indices])
+        expected_groups = [
+            [self.instances[4], self.instances[2]],
+            [self.instances[0], self.instances[1]],
+            [self.instances[3]],
+        ]
+        for idx, group in enumerate(grouped_instances):
+            assert group == expected_groups[idx]
+
     def test_guess_sorting_key_picks_the_longest_key(self):
         sampler = BucketBatchSampler(batch_size=2, padding_noise=0)
         instances = []