task: metadata: install: pip install -e .[all]
patch: diff --git a/src/eva/vision/data/datasets/_utils.py b/src/eva/vision/data/datasets/_utils.py
index 2d2fe30..1a17d7e 100644
--- a/src/eva/vision/data/datasets/_utils.py
+++ b/src/eva/vision/data/datasets/_utils.py
@@ -1,6 +1,6 @@
 """Dataset related function and helper functions."""
 
-from typing import List, Tuple
+from typing import List, Sequence, Tuple
 
 
 def indices_to_ranges(indices: List[int]) -> List[Tuple[int, int]]:
@@ -33,11 +33,11 @@ def indices_to_ranges(indices: List[int]) -> List[Tuple[int, int]]:
     return ranges
 
 
-def ranges_to_indices(ranges: List[Tuple[int, int]]) -> List[int]:
+def ranges_to_indices(ranges: Sequence[Tuple[int, int]]) -> List[int]:
     """Unpacks a list of ranges to individual indices.
 
     Args:
-        ranges: The list of ranges to produce the indices from.
+        ranges: A sequence of ranges to produce the indices from.
 
     Return:
         A list of the indices.
diff --git a/src/eva/vision/data/datasets/segmentation/total_segmentator.py b/src/eva/vision/data/datasets/segmentation/total_segmentator.py
index 4892e6b..92bb899 100644
--- a/src/eva/vision/data/datasets/segmentation/total_segmentator.py
+++ b/src/eva/vision/data/datasets/segmentation/total_segmentator.py
@@ -18,14 +18,14 @@ from eva.vision.utils import convert, io
 class TotalSegmentator2D(base.ImageSegmentation):
     """TotalSegmentator 2D segmentation dataset."""
 
-    _train_index_ranges: List[Tuple[int, int]] = [(0, 83)]
-    """Train range indices."""
+    _expected_dataset_lengths: Dict[str, int] = {
+        "train_small": 29892,
+        "val_small": 6480,
+    }
+    """Dataset version and split to the expected size."""
 
-    _val_index_ranges: List[Tuple[int, int]] = [(83, 103)]
-    """Validation range indices."""
-
-    _n_slices_per_image: int = 20
-    """The amount of slices to sample per 3D CT scan image."""
+    _sample_every_n_slices: int | None = None
+    """The amount of slices to sub-sample per 3D CT scan image."""
 
     _resources_full: List[structs.DownloadResource] = [
         structs.DownloadResource(
@@ -49,7 +49,7 @@ class TotalSegmentator2D(base.ImageSegmentation):
         self,
         root: str,
         split: Literal["train", "val"] | None,
-        version: Literal["small", "full"] = "small",
+        version: Literal["small", "full"] | None = "small",
         download: bool = False,
         as_uint8: bool = True,
         transforms: Callable | None = None,
@@ -60,7 +60,8 @@ class TotalSegmentator2D(base.ImageSegmentation):
             root: Path to the root directory of the dataset. The dataset will
                 be downloaded and extracted here, if it does not already exist.
             split: Dataset split to use. If `None`, the entire dataset is used.
-            version: The version of the dataset to initialize.
+            version: The version of the dataset to initialize. If `None`, it will
+                use the files located at root as is and wont perform any checks.
             download: Whether to download the data for the specified split.
                 Note that the download will be executed only by additionally
                 calling the :meth:`prepare_data` method and if the data does not
@@ -78,7 +79,7 @@ class TotalSegmentator2D(base.ImageSegmentation):
         self._as_uint8 = as_uint8
 
         self._samples_dirs: List[str] = []
-        self._indices: List[int] = []
+        self._indices: List[Tuple[int, int]] = []
 
     @functools.cached_property
     @override
@@ -99,7 +100,8 @@ class TotalSegmentator2D(base.ImageSegmentation):
 
     @override
     def filename(self, index: int) -> str:
-        sample_dir = self._samples_dirs[self._indices[index]]
+        sample_idx, _ = self._indices[index]
+        sample_dir = self._samples_dirs[sample_idx]
         return os.path.join(sample_dir, "ct.nii.gz")
 
     @override
@@ -114,21 +116,24 @@ class TotalSegmentator2D(base.ImageSegmentation):
 
     @override
     def validate(self) -> None:
+        if self._version is None:
+            return
+
         _validators.check_dataset_integrity(
             self,
-            length=1660 if self._split == "train" else 400,
+            length=self._expected_dataset_lengths.get(f"{self._split}_{self._version}", 0),
             n_classes=117,
             first_and_last_labels=("adrenal_gland_left", "vertebrae_T9"),
         )
 
     @override
     def __len__(self) -> int:
-        return len(self._indices) * self._n_slices_per_image
+        return len(self._indices)
 
     @override
     def load_image(self, index: int) -> tv_tensors.Image:
-        image_path = self._get_image_path(index)
-        slice_index = self._get_sample_slice_index(index)
+        sample_index, slice_index = self._indices[index]
+        image_path = self._get_image_path(sample_index)
         image_array = io.read_nifti_slice(image_path, slice_index)
         if self._as_uint8:
             image_array = convert.to_8bit(image_array)
@@ -137,8 +142,8 @@ class TotalSegmentator2D(base.ImageSegmentation):
 
     @override
     def load_mask(self, index: int) -> tv_tensors.Mask:
-        masks_dir = self._get_masks_dir(index)
-        slice_index = self._get_sample_slice_index(index)
+        sample_index, slice_index = self._indices[index]
+        masks_dir = self._get_masks_dir(sample_index)
         mask_paths = (os.path.join(masks_dir, label + ".nii.gz") for label in self.classes)
         one_hot_encoded = np.concatenate(
             [io.read_nifti_slice(path, slice_index) for path in mask_paths],
@@ -149,27 +154,20 @@ class TotalSegmentator2D(base.ImageSegmentation):
         segmentation_label = np.argmax(one_hot_encoded_with_bg, axis=2)
         return tv_tensors.Mask(segmentation_label)
 
-    def _get_masks_dir(self, index: int) -> str:
-        """Returns the directory of the corresponding masks."""
-        sample_dir = self._get_sample_dir(index)
-        return os.path.join(self._root, sample_dir, "segmentations")
-
-    def _get_image_path(self, index: int) -> str:
+    def _get_image_path(self, sample_index: int) -> str:
         """Returns the corresponding image path."""
-        sample_dir = self._get_sample_dir(index)
+        sample_dir = self._samples_dirs[sample_index]
         return os.path.join(self._root, sample_dir, "ct.nii.gz")
 
-    def _get_sample_dir(self, index: int) -> str:
-        """Returns the corresponding sample directory."""
-        sample_index = self._indices[index // self._n_slices_per_image]
-        return self._samples_dirs[sample_index]
+    def _get_masks_dir(self, sample_index: int) -> str:
+        """Returns the directory of the corresponding masks."""
+        sample_dir = self._samples_dirs[sample_index]
+        return os.path.join(self._root, sample_dir, "segmentations")
 
-    def _get_sample_slice_index(self, index: int) -> int:
-        """Returns the corresponding slice index."""
-        image_path = self._get_image_path(index)
-        total_slices = io.fetch_total_nifti_slices(image_path)
-        slice_indices = np.linspace(0, total_slices - 1, num=self._n_slices_per_image, dtype=int)
-        return slice_indices[index % self._n_slices_per_image]
+    def _get_number_of_slices_per_sample(self, sample_index: int) -> int:
+        """Returns the total amount of slices of a sample."""
+        image_path = self._get_image_path(sample_index)
+        return io.fetch_total_nifti_slices(image_path)
 
     def _fetch_samples_dirs(self) -> List[str]:
         """Returns the name of all the samples of all the splits of the dataset."""
@@ -180,29 +178,46 @@ class TotalSegmentator2D(base.ImageSegmentation):
         ]
         return sorted(sample_filenames)
 
-    def _create_indices(self) -> List[int]:
-        """Builds the dataset indices for the specified split."""
-        split_index_ranges = {
-            "train": self._train_index_ranges,
-            "val": self._val_index_ranges,
-            None: [(0, 103)],
-        }
-        index_ranges = split_index_ranges.get(self._split)
-        if index_ranges is None:
-            raise ValueError("Invalid data split. Use 'train', 'val' or `None`.")
+    def _get_split_indices(self) -> List[int]:
+        """Returns the samples indices that corresponding the dataset split and version."""
+        key = f"{self._split}_{self._version}"
+        match key:
+            case "train_small":
+                index_ranges = [(0, 83)]
+            case "val_small":
+                index_ranges = [(83, 102)]
+            case _:
+                index_ranges = [(0, len(self._samples_dirs))]
 
         return _utils.ranges_to_indices(index_ranges)
 
+    def _create_indices(self) -> List[Tuple[int, int]]:
+        """Builds the dataset indices for the specified split.
+
+        Returns:
+            A list of tuples, where the first value indicates the
+            sample index which the second its corresponding slice
+            index.
+        """
+        indices = [
+            (sample_idx, slide_idx)
+            for sample_idx in self._get_split_indices()
+            for slide_idx in range(self._get_number_of_slices_per_sample(sample_idx))
+            if slide_idx % (self._sample_every_n_slices or 1) == 0
+        ]
+        return indices
+
     def _download_dataset(self) -> None:
         """Downloads the dataset."""
         dataset_resources = {
             "small": self._resources_small,
             "full": self._resources_full,
-            None: (0, 103),
         }
-        resources = dataset_resources.get(self._version)
+        resources = dataset_resources.get(self._version or "")
         if resources is None:
-            raise ValueError("Invalid data version. Use 'small' or 'full'.")
+            raise ValueError(
+                f"Can't download data version '{self._version}'. Use 'small' or 'full'."
+            )
 
         for resource in resources:
             if os.path.isdir(self._root):

problem_statement: Update `TotalSegmentator2D` to fetch all the slides
Currently we sample every 20th slide from a 3d nifti file. We would like to update the dataset to fetch all
repo: kaiko-ai/eva
test_cmd: pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
test_patch: diff --git a/tests/eva/vision/data/datasets/segmentation/test_total_segmentator.py b/tests/eva/vision/data/datasets/segmentation/test_total_segmentator.py
index 3e7f09e..9607a2a 100644
--- a/tests/eva/vision/data/datasets/segmentation/test_total_segmentator.py
+++ b/tests/eva/vision/data/datasets/segmentation/test_total_segmentator.py
@@ -11,7 +11,7 @@ from eva.vision.data import datasets
 
 @pytest.mark.parametrize(
     "split, expected_length",
-    [("train", 1660), ("val", 400), (None, 2060)],
+    [("train", 9), ("val", 9), (None, 9)],
 )
 def test_length(
     total_segmentator_dataset: datasets.TotalSegmentator2D, expected_length: int
@@ -25,6 +25,7 @@ def test_length(
     [
         (None, 0),
         ("train", 0),
+        ("val", 0),
     ],
 )
 def test_sample(total_segmentator_dataset: datasets.TotalSegmentator2D, index: int) -> None:
@@ -43,7 +44,7 @@ def test_sample(total_segmentator_dataset: datasets.TotalSegmentator2D, index: i
 
 @pytest.fixture(scope="function")
 def total_segmentator_dataset(
-    split: Literal["train", "val"], assets_path: str
+    split: Literal["train", "val"] | None, assets_path: str
 ) -> datasets.TotalSegmentator2D:
     """TotalSegmentator2D dataset fixture."""
     dataset = datasets.TotalSegmentator2D(
@@ -55,6 +56,7 @@ def total_segmentator_dataset(
             "Totalsegmentator_dataset_v201",
         ),
         split=split,
+        version=None,
     )
     dataset.prepare_data()
     dataset.configure()