diff --git a/CHANGELOG.md b/CHANGELOG.md
index acf87eff..e12e0d8f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,9 @@ Keep it human-readable, your future self will thank you!
 
 ### Added
 ### Changed
+
+- Added incremental building of datasets
+
 ### Removed
 
 ## [0.4.5]
diff --git a/src/anemoi/datasets/commands/init.py b/src/anemoi/datasets/commands/init.py
index b83d5033..d03d61a0 100644
--- a/src/anemoi/datasets/commands/init.py
+++ b/src/anemoi/datasets/commands/init.py
@@ -16,36 +16,37 @@ class Init(Command):
     internal = True
     timestamp = True
 
-    def add_arguments(self, init):
+    def add_arguments(self, subparser):
 
-        init.add_argument("config", help="Configuration yaml file defining the recipe to create the dataset.")
-        init.add_argument("path", help="Path to store the created data.")
+        subparser.add_argument("config", help="Configuration yaml file defining the recipe to create the dataset.")
+        subparser.add_argument("path", help="Path to store the created data.")
 
-        init.add_argument(
+        subparser.add_argument(
             "--overwrite",
             action="store_true",
             help="Overwrite existing files. This will delete the target dataset if it already exists.",
         )
-        init.add_argument(
+        subparser.add_argument(
             "--test",
             action="store_true",
             help="Build a small dataset, using only the first dates. And, when possible, using low resolution and less ensemble members.",
         )
-        init.add_argument(
+        subparser.add_argument(
             "--check-name",
             dest="check_name",
             action="store_true",
             help="Check if the dataset name is valid before creating it.",
         )
-        init.add_argument(
+        subparser.add_argument(
             "--no-check-name",
             dest="check_name",
             action="store_false",
             help="Do not check if the dataset name is valid before creating it.",
         )
-        init.set_defaults(check_name=False)
+        subparser.set_defaults(check_name=False)
+        subparser.add_argument("--cache", help="Location to store the downloaded data.", metavar="DIR")
 
-        init.add_argument("--trace", action="store_true")
+        subparser.add_argument("--trace", action="store_true")
 
     def run(self, args):
         options = vars(args)
diff --git a/src/anemoi/datasets/commands/load.py b/src/anemoi/datasets/commands/load.py
index adb4f7ff..d776ea10 100644
--- a/src/anemoi/datasets/commands/load.py
+++ b/src/anemoi/datasets/commands/load.py
@@ -25,6 +25,7 @@ def add_arguments(self, subparser):
         #    )
 
         subparser.add_argument("path", help="Path to store the created data.")
+        subparser.add_argument("--cache", help="Location to store the downloaded data.", metavar="DIR")
         subparser.add_argument("--trace", action="store_true")
 
     def run(self, args):
diff --git a/src/anemoi/datasets/create/__init__.py b/src/anemoi/datasets/create/__init__.py
index d4a2f504..d12df1ba 100644
--- a/src/anemoi/datasets/create/__init__.py
+++ b/src/anemoi/datasets/create/__init__.py
@@ -203,14 +203,14 @@ def __init__(self, path, overwrite=False):
 
 
 class Actor:  # TODO: rename to Creator
-    cache = None
     dataset_class = WritableDataset
 
-    def __init__(self, path):
+    def __init__(self, path, cache=None):
         # Catch all floating point errors, including overflow, sqrt(<0), etc
         np.seterr(all="raise", under="warn")
 
         self.path = path
+        self.cache = cache
         self.dataset = self.dataset_class(self.path)
 
     def run(self):
@@ -325,11 +325,11 @@ def build_input_(main_config, output_config):
 
 class Init(Actor, HasRegistryMixin, HasStatisticTempMixin, HasElementForDataMixin):
     dataset_class = NewDataset
-    def __init__(self, path, config, check_name=False, overwrite=False, use_threads=False, statistics_temp_dir=None, progress=None, test=False, **kwargs):  # fmt: skip
+    def __init__(self, path, config, check_name=False, overwrite=False, use_threads=False, statistics_temp_dir=None, progress=None, test=False, cache=None, **kwargs):  # fmt: skip
         if _path_readable(path) and not overwrite:
             raise Exception(f"{self.path} already exists. Use overwrite=True to overwrite.")
 
-        super().__init__(path)
+        super().__init__(path, cache=cache)
         self.config = config
         self.check_name = check_name
         self.use_threads = use_threads
@@ -497,8 +497,8 @@ def sanity_check_config(a, b):
 
 
 class Load(Actor, HasRegistryMixin, HasStatisticTempMixin, HasElementForDataMixin):
-    def __init__(self, path, parts=None,  use_threads=False, statistics_temp_dir=None, progress=None, **kwargs):  # fmt: skip
-        super().__init__(path)
+    def __init__(self, path, parts=None,  use_threads=False, statistics_temp_dir=None, progress=None, cache=None, **kwargs):  # fmt: skip
+        super().__init__(path, cache=cache)
         self.use_threads = use_threads
         self.statistics_temp_dir = statistics_temp_dir
         self.progress = progress
diff --git a/src/anemoi/datasets/create/config.py b/src/anemoi/datasets/create/config.py
index 6f0bad53..e292a6e5 100644
--- a/src/anemoi/datasets/create/config.py
+++ b/src/anemoi/datasets/create/config.py
@@ -16,6 +16,8 @@
 from anemoi.utils.config import load_any_dict_format
 from earthkit.data.core.order import normalize_order_by
 
+from anemoi.datasets.dates.groups import Groups
+
 LOG = logging.getLogger(__name__)
 
 
@@ -212,11 +214,11 @@ def _prepare_serialisation(o):
 def set_to_test_mode(cfg):
     NUMBER_OF_DATES = 4
 
-    dates = cfg.dates
+    dates = cfg["dates"]
     LOG.warn(f"Running in test mode. Changing the list of dates to use only {NUMBER_OF_DATES}.")
-    groups = Groups(**cfg.dates)
+    groups = Groups(**LoadersConfig(cfg).dates)
     dates = groups.dates
-    cfg.dates = dict(
+    cfg["dates"] = dict(
         start=dates[0],
         end=dates[NUMBER_OF_DATES - 1],
         frequency=dates.frequency,
@@ -250,16 +252,22 @@ def set_element_to_test(obj):
 
 def loader_config(config, is_test=False):
     config = Config(config)
-    obj = LoadersConfig(config)
     if is_test:
-        obj = set_to_test_mode(obj)
+        set_to_test_mode(config)
+    obj = LoadersConfig(config)
 
     # yaml round trip to check that serialisation works as expected
     copy = obj.get_serialisable_dict()
     copy = yaml.load(yaml.dump(copy), Loader=yaml.SafeLoader)
     copy = Config(copy)
     copy = LoadersConfig(config)
-    assert yaml.dump(obj) == yaml.dump(copy), (obj, copy)
+
+    a = yaml.dump(obj)
+    b = yaml.dump(copy)
+    if a != b:
+        print(a)
+        print(b)
+        raise ValueError("Serialisation failed")
 
     return copy
 
diff --git a/src/anemoi/datasets/data/dataset.py b/src/anemoi/datasets/data/dataset.py
index 2dfc9816..2e95ec4f 100644
--- a/src/anemoi/datasets/data/dataset.py
+++ b/src/anemoi/datasets/data/dataset.py
@@ -216,7 +216,7 @@ def metadata(self):
         import anemoi
 
         def tidy(v):
-            if isinstance(v, (list, tuple)):
+            if isinstance(v, (list, tuple, set)):
                 return [tidy(i) for i in v]
             if isinstance(v, dict):
                 return {k: tidy(v) for k, v in v.items()}
diff --git a/src/anemoi/datasets/data/subset.py b/src/anemoi/datasets/data/subset.py
index 3ace75be..3c36a0c2 100644
--- a/src/anemoi/datasets/data/subset.py
+++ b/src/anemoi/datasets/data/subset.py
@@ -111,10 +111,8 @@ def _get_slice(self, s):
     @expand_list_indexing
     def _get_tuple(self, n):
         index, changes = index_to_slices(n, self.shape)
-        # print('INDEX', index, changes)
         indices = [self.indices[i] for i in range(*index[0].indices(self._len))]
         indices = make_slice_or_index_from_list_or_tuple(indices)
-        # print('INDICES', indices)
         index, _ = update_tuple(index, 0, indices)
         result = self.dataset[index]
         result = apply_index_to_slices_changes(result, changes)
diff --git a/tests/test_data.py b/tests/test_data.py
index 42e2a001..2925aa8c 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -861,6 +861,18 @@ def test_dates():
     assert as_last_date("2021-01-01", dates) == np.datetime64("2021-01-01T23:59:59")
 
 
+@mockup_open_zarr
+def test_dates_using_list():
+    dates = [np.datetime64("2021-01-01T00:00:00") + i * np.timedelta64(6, "h") for i in range(3, 365 * 4 - 2)]
+    assert dates[0] == np.datetime64("2021-01-01T18:00:00")
+    assert dates[-1] == np.datetime64("2021-12-31T06:00:00")
+
+    assert as_first_date(2021, dates) == np.datetime64("2021-01-01T18:00:00")
+    assert as_last_date(2021, dates) == np.datetime64("2021-12-31T06:00:00")
+    assert as_first_date("2021", dates) == np.datetime64("2021-01-01T18:00:00")
+    assert as_last_date("2021", dates) == np.datetime64("2021-12-31T06:00:00")
+
+
 @mockup_open_zarr
 def test_slice_1():
     test = DatasetTester("test-2021-2021-6h-o96-abcd")