Shuffle train subset for summarization example (#3909)

* Shuffle train subset

* Cleaner shuffle

examples/summarization/bart/finetune.py

@@ -102,13 +102,13 @@ class SummarizationTrainer(BaseTransformer):
 
         return self.test_end(outputs)
 
-    def get_dataloader(self, type_path: str, batch_size: int) -> DataLoader:
+    def get_dataloader(self, type_path: str, batch_size: int, shuffle: bool = False) -> DataLoader:
         dataset = SummarizationDataset(self.tokenizer, type_path=type_path, **self.dataset_kwargs)
-        dataloader = DataLoader(dataset, batch_size=batch_size, collate_fn=dataset.collate_fn)
+        dataloader = DataLoader(dataset, batch_size=batch_size, collate_fn=dataset.collate_fn, shuffle=shuffle)
         return dataloader
 
     def train_dataloader(self) -> DataLoader:
-        dataloader = self.get_dataloader("train", batch_size=self.hparams.train_batch_size)
+        dataloader = self.get_dataloader("train", batch_size=self.hparams.train_batch_size, shuffle=True)
         t_total = (
             (len(dataloader.dataset) // (self.hparams.train_batch_size * max(1, self.hparams.n_gpu)))
             // self.hparams.gradient_accumulation_steps