wip flex block mask creation

src/axolotl/utils/collators/batching.py

@@ -169,19 +169,26 @@ class FlexBatchSamplerDataCollatorForSeq2Seq(DataCollatorForSeq2Seq):
                 if feature == "length":
                     continue
                 if feature == "attention_mask":
-                    seq_len_list = [
-                        get_seqlens_from_pos_ids(item["position_ids"])
-                        for item in features_
+                    arrays = [
+                        (i + 1) * np.array(item[feature])
+                        for i, item in enumerate(features_)
                         if feature in item
                     ]
-
-                    out_features[i][feature] = np.concatenate(seq_len_list)
+                    out_features[i][feature] = np.concatenate(arrays)
                 else:
                     arrays = [
                         np.array(item[feature]) for item in features_ if feature in item
                     ]
                     out_features[i][feature] = np.concatenate(arrays)
-        return super().__call__(out_features, return_tensors=return_tensors)
+        out = super().__call__(out_features, return_tensors=return_tensors)
+
+        collated_seq_lens = get_seqlens_from_pos_ids(out["position_ids"])
+
+        doc_mask = 
+
+        out["attention_mask"] 
+
+        return out
 
 
 @dataclass