Enable loading train and val split in JSON data module

litgpt/data/json.py

@@ -3,7 +3,7 @@
 import json
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Optional, Union
+from typing import Optional, Union, Tuple, Any
 
 import torch
 from torch.utils.data import random_split, DataLoader
@@ -18,13 +18,14 @@ class JSON(LitDataModule):
     """Loads JSON data for supervised finetuning."""
 
     json_path: Path
-    """A path to a JSON file containing the data. The file should contain a list of samples (dicts).
-    Each dict must have the keys 'instruction' and 'output', and can optionally have a key 'input'
-    (see Alpaca)."""
+    """A path to a JSON file or a directory with `train.json` and `val.json` containing the data. 
+    The file(s) should contain a list of samples (dicts). Each dict must have the keys 'instruction' and 'output', 
+    and can optionally have a key 'input' (see Alpaca)."""
     mask_prompt: bool = False
     """Whether to mask the prompt section from the label (with ``ignore_index``)."""
-    test_split_fraction: float = 0.1
-    """The fraction of the dataset to use for the test/validation dataset. The rest is used for training."""
+    test_split_fraction: Optional[float] = None
+    """The fraction of the dataset to use for the validation dataset. The rest is used for training.
+    Only applies if you passed in a single file to `json_path`."""
     prompt_style: Union[str, PromptStyle] = "alpaca"
     """The style to apply to instruction prompts. See `litgpt.prompts` for a list of available styles."""
     ignore_index: int = -1
@@ -41,8 +42,16 @@ class JSON(LitDataModule):
     test_dataset: Optional[SFTDataset] = field(default=None, init=False, repr=False)
 
     def __post_init__(self):
-        if not self.json_path.is_file():
-            raise FileNotFoundError(f"The file {self.json_path} does not exist.")
+        if self.json_path.is_dir() and self.test_split_fraction is not None:
+            raise ValueError(
+                "If `json_path` is a directory, it must contain 'train.json' and 'val.json' files and"
+                f" hence `test_split_fraction` should not be set. Got `{self.test_split_fraction=}`."
+            )
+        if not self.json_path.exists():
+            raise FileNotFoundError(
+                "The `json_path` must be a file or a directory containing 'train.json' and 'val.json' files,"
+                f" but '{self.json_path!s}' does not exist."
+            )
         if isinstance(self.prompt_style, str):
             self.prompt_style = PromptStyle.from_name(self.prompt_style)
 
@@ -57,16 +66,7 @@ def connect(
         self.max_seq_length = -1 if max_seq_length is None else max_seq_length
 
     def setup(self, stage: str = "") -> None:
-        with open(self.json_path, "r", encoding="utf-8") as file:
-            data = json.load(file)
-
-        # Partition the dataset into train and test
-        train_data, test_data = random_split(
-            data,
-            [1.0 - self.test_split_fraction, self.test_split_fraction],
-            generator=torch.Generator().manual_seed(self.seed)
-        )
-        train_data, test_data = list(train_data), list(test_data)
+        train_data, test_data = self.get_splits()
 
         self.train_dataset = SFTDataset(
             data=train_data,
@@ -103,3 +103,31 @@ def val_dataloader(self) -> DataLoader:
             num_workers=self.num_workers,
             collate_fn=get_sft_collate_fn(max_seq_length=self.max_seq_length, ignore_index=self.ignore_index)
         )
+
+    def get_splits(self) -> Tuple:
+        # A single file (gets split into train and test)
+        if self.json_path.is_file():
+            data = load_split(self.json_path)
+
+            # Partition the dataset into train and test
+            train_data, test_data = random_split(
+                data,
+                [1.0 - self.test_split_fraction, self.test_split_fraction],
+                generator=torch.Generator().manual_seed(self.seed)
+            )
+            return train_data, test_data
+
+        # A directory containing train.json and val.json
+        if (self.json_path / "train.json").is_file() and (self.json_path / f"val.json").is_file():
+            train_data = load_split(self.json_path / "train.json")
+            test_data = load_split(self.json_path / f"val.json")
+            return train_data, test_data
+
+        raise FileNotFoundError(
+            "The `json_path` must be a file or a directory containing 'train.json' and 'val.json' files."
+        )
+
+
+def load_split(json_path: Path) -> Any:
+    with open(json_path, "r", encoding="utf-8") as file:
+        return json.load(file)

tests/data/test_json.py

@@ -24,10 +24,6 @@ def apply(self, prompt, **kwargs):
     with open(json_path, "w", encoding="utf-8") as fp:
         json.dump(mock_data, fp)
 
-    with pytest.raises(FileNotFoundError):
-        JSON(tmp_path / "not exist")
-
-    # TODO: Make prompt template an argumenet
     data = JSON(json_path, test_split_fraction=0.5, prompt_style=Style(), num_workers=0)
     data.connect(tokenizer=mock_tokenizer, batch_size=2)
     data.prepare_data()  # does nothing
@@ -58,3 +54,53 @@ def apply(self, prompt, **kwargs):
     assert isinstance(train_dataloader.dataset.prompt_style, Style)
     assert isinstance(val_dataloader.dataset.prompt_style, Style)
 
+
+def test_json_input_validation(tmp_path):
+    from litgpt.data import JSON
+
+    with pytest.raises(FileNotFoundError, match="The `json_path` must be a file or a directory"):
+        JSON(tmp_path / "not exist")
+
+    with pytest.raises(ValueError, match="`test_split_fraction` should not be set"):
+        JSON(tmp_path, test_split_fraction=0.5)
+
+    data = JSON(tmp_path)
+    data.prepare_data()  # does nothing
+
+    # Empty directory
+    with pytest.raises(FileNotFoundError, match="must be a file or a directory containing"):
+        data.setup()
+
+    # Only train.json exists
+    (tmp_path / "train.json").touch()
+    with pytest.raises(FileNotFoundError, match="must be a file or a directory containing"):
+        data.setup()
+
+
+def test_json_with_splits(tmp_path, mock_tokenizer):
+    from litgpt.data import JSON
+
+    mock_train_data = [
+        {"instruction": "Add", "input": "2+2", "output": "4"},
+        {"instruction": "Subtract", "input": "5-3", "output": "2"},
+        {"instruction": "Exponentiate", "input": "2^3", "output": "8"},
+    ]
+    mock_test_data = [
+        {"instruction": "Multiply", "input": "6*4", "output": "24"},
+        {"instruction": "Divide", "input": "10/2", "output": "5"},
+    ]
+    with open(tmp_path / "train.json", "w", encoding="utf-8") as fp:
+        json.dump(mock_train_data, fp)
+    with open(tmp_path / "val.json", "w", encoding="utf-8") as fp:
+        json.dump(mock_test_data, fp)
+
+    data = JSON(tmp_path, num_workers=0)
+    data.connect(tokenizer=mock_tokenizer, batch_size=2)
+    data.prepare_data()  # does nothing
+    data.setup()
+
+    train_dataloader = data.train_dataloader()
+    val_dataloader = data.val_dataloader()
+
+    assert len(train_dataloader) == 2
+    assert len(val_dataloader) == 1

tutorials/prepare_dataset.md

@@ -366,6 +366,8 @@ python litgpt/finetune/lora.py \
   --checkpoint_dir "checkpoints/tiiuae/falcon-7b"
 ```
 
+You can also pass a directory containing a `train.json` and `val.json` to `--data.json_path` to define a fixed train/val split.
+
  
 
 ### Preparing Custom Datasets Using LitDataModule