From b457ea910efafad82f5bac93ea2ca9ee93650511 Mon Sep 17 00:00:00 2001
From: Devin Zhou <xinzhou1@meta.com>
Date: Tue, 13 Jun 2023 11:04:17 -0700
Subject: [PATCH] Enable Class Balancing for Model Train Sampler

Summary:
X-link: https://github.com/facebookresearch/detectron2/pull/4995

Pull Request resolved: https://github.com/facebookresearch/d2go/pull/570

Differential Revision: D46377371

fbshipit-source-id: c547997c71152d75011cbe94a0c762d20aa33669
---
 d2go/data/build.py | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/d2go/data/build.py b/d2go/data/build.py
index f5606f31..682d01a5 100644
--- a/d2go/data/build.py
+++ b/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 +105,27 @@ 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:
+        """
+        1. Calculate repeat factors using category frequency for each dataset.
+        2. Element wise dot producting the dataset frequency repeat factors with
+            the category frequency repeat factors gives the final repeat factors.
+        """
+        category_repeat_factors = [
+            RepeatFactorTrainingSampler.repeat_factors_from_category_frequency(
+                dataset_dict, cfg.DATALOADER.REPEAT_THRESHOLD
+            )
+            for dataset_dict in dataset_name_to_dicts.values()
+        ]
+        # flatten the category repeat factors from all datasets
+        category_repeat_factors = list(
+            itertools.chain.from_iterable(category_repeat_factors)
+        )
+        repeat_factors = torch.mul(category_repeat_factors, repeat_factors)
+        repeat_factors = repeat_factors / torch.min(repeat_factors)
+
+    sampler = RepeatFactorTrainingSampler(repeat_factors)
 
     return build_batch_data_loader(
         dataset,
@@ -149,7 +171,13 @@ 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_category_balance=True
+        )
     else:
         data_loader = build_detection_train_loader(cfg, mapper=mapper)
     return data_loader