Enable Class Balancing for Model Train Sampler

Summary:
X-link: facebookresearch/detectron2#4995

Pull Request resolved: facebookresearch#570

Differential Revision: D46377371

fbshipit-source-id: 76c3bca2fc33056669c0952056668456aaf55ca0

d2go/data/build.py

@@ -66,7 +66,9 @@ def get_train_datasets_repeat_factors(cfg: CfgNode) -> Dict[str, float]:
     return name_to_weight
 
 
-def build_weighted_detection_train_loader(cfg: CfgNode, mapper=None):
+def build_weighted_detection_train_loader(
+    cfg: CfgNode, mapper=None, enable_category_balance=False
+):
     dataset_repeat_factors = get_train_datasets_repeat_factors(cfg)
     # OrderedDict to guarantee order of values() consistent with repeat factors
     dataset_name_to_dicts = OrderedDict(
@@ -103,7 +105,22 @@ def build_weighted_detection_train_loader(cfg: CfgNode, mapper=None):
             cfg.DATASETS.TRAIN_REPEAT_FACTOR
         )
     )
-    sampler = RepeatFactorTrainingSampler(torch.tensor(repeat_factors))
+    repeat_factors = torch.tensor(repeat_factors)
+    if enable_category_balance:
+        """
+        Current repeat factor is already balanced by dataset frequency
+        Use annotations information in dataset_dicts to compute repeat factors to balance category frequencies.
+        Element wise dot producting these two list of repeat factors gives the final balanced repeat factors
+        """
+        class_balance_repeat_factors = (
+            RepeatFactorTrainingSampler.repeat_factors_from_category_frequency(
+                dataset_dicts, cfg.DATALOADER.REPEAT_THRESHOLD
+            )
+        )
+        repeat_factors = torch.mul(class_balance_repeat_factors, repeat_factors)
+        repeat_factors = repeat_factors / torch.min(repeat_factors)
+
+    sampler = RepeatFactorTrainingSampler(repeat_factors)
 
     return build_batch_data_loader(
         dataset,
@@ -149,7 +166,13 @@ def build_clip_grouping_data_loader(dataset, sampler, total_batch_size, num_work
 @fb_overwritable()
 def build_mapped_train_loader(cfg, mapper):
     if cfg.DATALOADER.SAMPLER_TRAIN == "WeightedTrainingSampler":
+        # balancing only datasets frequencies
         data_loader = build_weighted_detection_train_loader(cfg, mapper=mapper)
+    elif cfg.DATALOADER.SAMPLER_TRAIN == "WeightedCategoryTrainingSampler":
+        # balancing both datasets and its categories
+        data_loader = build_weighted_detection_train_loader(
+            cfg, mapper=mapper, enable_class_balance=True
+        )
     else:
         data_loader = build_detection_train_loader(cfg, mapper=mapper)
     return data_loader