Repository: pangeo-forge/pangeo-forge-recipes (python)

Issue:
Define dynamic target chunks interface in `StoreToZarr`
As discussed in https://github.com/pangeo-forge/pangeo-forge-recipes/pull/546#issuecomment-1688854651, I think we should give users the option of bringing their own dynamic chunking function to generate target chunks from a schema in StoreToZarr. The linked comment contains a pseudocode example. This is an alternative to merging #546 into `pangeo-forge-recipes`, based on @jbusecke and my recognition that:

1. Users may want to define their own dynamic chunking approach; and
2. #546 is a _lot_ of code to maintain in this repo, probably too much for right now

Pull request:
Dynamic chunking interface for StoreToZarr
Closes #572
Supersedes #546

@jbusecke, can you test drive this? You should be able to repurpose your work in #546 as follows:

```python
from pangeo_forge_recipes.transforms import StoreToZarr

from dynamic_target_chunks import dynamic_target_chunks_from_schema

kws = dict(
    target_chunk_size=...,
    target_chunks_aspect_ratio=...,
    size_tolerance=...,
    default_ratio=...,
    allow_extra_dims=...,
    allow_fallback_algo=...,
)

recipe = (
    ...
    | StoreToZarr(
        ...,
        dynamic_chunking_fn=dynamic_target_chunks_from_schema,
        dynamic_chunking_fn_kwargs=kws,
    )
)
```
In order to import `dynamic_target_chunks_from_schema` from a local module, you would need https://github.com/pangeo-forge/pangeo-forge-runner/issues/92 (feel free to work on that! 😄 ). Alternatively, you could:

- _**tired**_ 🥱 define `dynamic_target_chunks_from_schema` at the top of your recipe module
- _**wired**_ 🤪  release a package containing `dynamic_target_chunks_from_schema` on PyPI and add it to requirements.txt
- _**inspired**_ 🧘 push a package containing `dynamic_target_chunks_from_schema` to GitHub and install in in requirements.txt with `git+...`. This seems like the best short-term compromise between effort + effectiveness.

Patch:
diff --git a/docs/release_notes.md b/docs/release_notes.md
index ccf43b0..83066d4 100644
--- a/docs/release_notes.md
+++ b/docs/release_notes.md
@@ -1,5 +1,9 @@
 # Release Notes
 
+## v0.10.4 - 2023-11-15
+
+- Add `dynamic_chunking_fn`/`dynamic_chunking_fn_kwargs` keywords to StoreToZarr. This allows users to pass a function that will be called at runtime to determine the target chunks for the resulting datasets based on the in memory representation/size of the recipe dataset. {pull}`595`
+
 ## v0.10.3 - 2023-10-03
 
 - Assign injection spec values for command line interface {pull}`566`
diff --git a/examples/feedstock/gpcp_from_gcs.py b/examples/feedstock/gpcp_from_gcs.py
index caea9a1..9b13d59 100644
--- a/examples/feedstock/gpcp_from_gcs.py
+++ b/examples/feedstock/gpcp_from_gcs.py
@@ -29,6 +29,9 @@ def test_ds(store: zarr.storage.FSStore) -> zarr.storage.FSStore:
     assert ds.title == (
         "Global Precipitation Climatatology Project (GPCP) " "Climate Data Record (CDR), Daily V1.3"
     )
+    # Making sure that the native chunking is different from the dynamic chunking
+    assert ds.chunks["time"][0] == 1
+
     return store
 
 
diff --git a/examples/feedstock/gpcp_from_gcs_dynamic_chunks.py b/examples/feedstock/gpcp_from_gcs_dynamic_chunks.py
new file mode 100644
index 0000000..bc9c3fd
--- /dev/null
+++ b/examples/feedstock/gpcp_from_gcs_dynamic_chunks.py
@@ -0,0 +1,54 @@
+from typing import Dict
+
+import apache_beam as beam
+import pandas as pd
+import xarray as xr
+import zarr
+
+from pangeo_forge_recipes.patterns import ConcatDim, FilePattern
+from pangeo_forge_recipes.transforms import OpenURLWithFSSpec, OpenWithXarray, StoreToZarr
+
+dates = [
+    d.to_pydatetime().strftime("%Y%m%d")
+    for d in pd.date_range("1996-10-01", "1999-02-01", freq="D")
+]
+
+
+def make_url(time):
+    url_base = "https://storage.googleapis.com/pforge-test-data"
+    return f"{url_base}/gpcp/v01r03_daily_d{time}.nc"
+
+
+concat_dim = ConcatDim("time", dates, nitems_per_file=1)
+pattern = FilePattern(make_url, concat_dim)
+
+
+def test_ds(store: zarr.storage.FSStore) -> zarr.storage.FSStore:
+    # This fails integration test if not imported here
+    # TODO: see if --setup-file option for runner fixes this
+    import xarray as xr
+
+    ds = xr.open_dataset(store, engine="zarr", chunks={})
+    assert ds.title == (
+        "Global Precipitation Climatatology Project (GPCP) " "Climate Data Record (CDR), Daily V1.3"
+    )
+
+    assert ds.chunks["time"][0] == 2
+    return store
+
+
+def chunk_func(ds: xr.Dataset) -> Dict[str, int]:
+    return {"time": 2}
+
+
+recipe = (
+    beam.Create(pattern.items())
+    | OpenURLWithFSSpec()
+    | OpenWithXarray(file_type=pattern.file_type, xarray_open_kwargs={"decode_coords": "all"})
+    | StoreToZarr(
+        dynamic_chunking_fn=chunk_func,
+        store_name="gpcp.zarr",
+        combine_dims=pattern.combine_dim_keys,
+    )
+    | "Test dataset" >> beam.Map(test_ds)
+)
diff --git a/examples/feedstock/meta.yaml b/examples/feedstock/meta.yaml
index cb9f294..29fc5db 100644
--- a/examples/feedstock/meta.yaml
+++ b/examples/feedstock/meta.yaml
@@ -1,6 +1,8 @@
 recipes:
   - id: "gpcp-from-gcs"
     object: "gpcp_from_gcs:recipe"
+  - id: "gpcp-from-gcs-dynamic-chunks"
+    object: "gpcp_from_gcs_dynamic_chunks:recipe"
   - id: "noaa-oisst"
     object: "noaa_oisst:recipe"
   - id: "terraclimate"
diff --git a/pangeo_forge_recipes/transforms.py b/pangeo_forge_recipes/transforms.py
index 3f4c390..0e12168 100644
--- a/pangeo_forge_recipes/transforms.py
+++ b/pangeo_forge_recipes/transforms.py
@@ -17,7 +17,7 @@ import apache_beam as beam
 import xarray as xr
 import zarr
 
-from .aggregation import XarraySchema, dataset_to_schema, schema_to_zarr
+from .aggregation import XarraySchema, dataset_to_schema, schema_to_template_ds, schema_to_zarr
 from .combiners import CombineMultiZarrToZarr, CombineXarraySchemas
 from .openers import open_url, open_with_kerchunk, open_with_xarray
 from .patterns import CombineOp, Dimension, FileType, Index, augment_index_with_start_stop
@@ -505,7 +505,14 @@ class StoreToZarr(beam.PTransform, ZarrWriterMixin):
     :param target_root: Root path the Zarr store will be created inside;
         `store_name` will be appended to this prefix to create a full path.
     :param target_chunks: Dictionary mapping dimension names to chunks sizes.
-        If a dimension is a not named, the chunks will be inferred from the data.
+      If a dimension is a not named, the chunks will be inferred from the data.
+    :param dynamic_chunking_fn: Optionally provide a function that takes an ``xarray.Dataset``
+      template dataset as its first argument and returns a dynamically generated chunking dict.
+      If provided, ``target_chunks`` cannot also be passed. You can use this to determine chunking
+      based on the full dataset (e.g. divide along a certain dimension based on a desired chunk
+      size in memory). For more advanced chunking strategies, check
+      out https://github.com/jbusecke/dynamic_chunks
+    :param dynamic_chunking_fn_kwargs: Optional keyword arguments for ``dynamic_chunking_fn``.
     :param attrs: Extra group-level attributes to inject into the dataset.
     """
 
@@ -517,19 +524,34 @@ class StoreToZarr(beam.PTransform, ZarrWriterMixin):
         default_factory=RequiredAtRuntimeDefault
     )
     target_chunks: Dict[str, int] = field(default_factory=dict)
+    dynamic_chunking_fn: Optional[Callable[[xr.Dataset], dict]] = None
+    dynamic_chunking_fn_kwargs: Optional[dict] = field(default_factory=dict)
     attrs: Dict[str, str] = field(default_factory=dict)
 
+    def __post_init__(self):
+        if self.target_chunks and self.dynamic_chunking_fn:
+            raise ValueError("Passing both `target_chunks` and `dynamic_chunking_fn` not allowed.")
+
     def expand(
         self,
         datasets: beam.PCollection[Tuple[Index, xr.Dataset]],
     ) -> beam.PCollection[zarr.storage.FSStore]:
         schema = datasets | DetermineSchema(combine_dims=self.combine_dims)
         indexed_datasets = datasets | IndexItems(schema=schema)
-        rechunked_datasets = indexed_datasets | Rechunk(
-            target_chunks=self.target_chunks, schema=schema
+        target_chunks = (
+            self.target_chunks
+            if not self.dynamic_chunking_fn
+            else beam.pvalue.AsSingleton(
+                schema
+                | beam.Map(schema_to_template_ds)
+                | beam.Map(self.dynamic_chunking_fn, **self.dynamic_chunking_fn_kwargs)
+            )
         )
+        rechunked_datasets = indexed_datasets | Rechunk(target_chunks=target_chunks, schema=schema)
         target_store = schema | PrepareZarrTarget(
-            target=self.get_full_target(), target_chunks=self.target_chunks, attrs=self.attrs
+            target=self.get_full_target(),
+            target_chunks=target_chunks,
+            attrs=self.attrs,
         )
         n_target_stores = rechunked_datasets | StoreDatasetFragments(target_store=target_store)
         singleton_target_store = (


Test patch:
diff --git a/.github/workflows/test-integration.yaml b/.github/workflows/test-integration.yaml
index 6616f3e..ef10be9 100644
--- a/.github/workflows/test-integration.yaml
+++ b/.github/workflows/test-integration.yaml
@@ -57,8 +57,11 @@ jobs:
       - name: 🌈 Install pangeo-forge-recipes & pangeo-forge-runner
         shell: bash -l {0}
         run: |
-          python -m pip install -e ".[test,minio]"
           python -m pip install ${{ matrix.runner-version }}
+          python -m pip install -e ".[test,minio]"
+
+        # order reversed to fix https://github.com/pangeo-forge/pangeo-forge-recipes/pull/595#issuecomment-1811630921
+        # this should however be fixed in the runner itself
       - name: 🏄‍♂️ Run Tests
         shell: bash -l {0}
         run: |
diff --git a/tests/test_transforms.py b/tests/test_transforms.py
index e40f77c..fb698e3 100644
--- a/tests/test_transforms.py
+++ b/tests/test_transforms.py
@@ -234,18 +234,20 @@ def test_rechunk(
         assert_that(rechunked, correct_chunks())
 
 
+class OpenZarrStore(beam.PTransform):
+    @staticmethod
+    def _open_zarr(store):
+        return xr.open_dataset(store, engine="zarr", chunks={})
+
+    def expand(self, pcoll):
+        return pcoll | beam.Map(self._open_zarr)
+
+
 def test_StoreToZarr_emits_openable_fsstore(
     pipeline,
     netcdf_local_file_pattern_sequential,
     tmp_target_url,
 ):
-    def _open_zarr(store):
-        return xr.open_dataset(store, engine="zarr")
-
-    class OpenZarrStore(beam.PTransform):
-        def expand(self, pcoll):
-            return pcoll | beam.Map(_open_zarr)
-
     def is_xrdataset():
         def _is_xr_dataset(actual):
             assert len(actual) == 1
@@ -266,6 +268,75 @@ def test_StoreToZarr_emits_openable_fsstore(
         assert_that(open_store, is_xrdataset())
 
 
+@pytest.mark.parametrize("with_kws", [True, False])
+def test_StoreToZarr_dynamic_chunking_interface(
+    pipeline: beam.Pipeline,
+    netcdf_local_file_pattern_sequential: FilePattern,
+    tmp_target_url: str,
+    daily_xarray_dataset: xr.Dataset,
+    with_kws: bool,
+):
+    def has_dynamically_set_chunks():
+        def _has_dynamically_set_chunks(actual):
+            assert len(actual) == 1
+            item = actual[0]
+            assert isinstance(item, xr.Dataset)
+            if not with_kws:
+                # we've dynamically set the number of timesteps per chunk to be equal to
+                # the length of the full time dimension of the aggregate dataset, therefore
+                # if this worked, there should only be one chunk
+                assert len(item.chunks["time"]) == 1
+            else:
+                # in this case, we've passed the kws {"divisor": 2}, so we expect two time chunks
+                assert len(item.chunks["time"]) == 2
+
+        return _has_dynamically_set_chunks
+
+    pattern: FilePattern = netcdf_local_file_pattern_sequential
+
+    time_len = len(daily_xarray_dataset.time)
+
+    def dynamic_chunking_fn(template_ds: xr.Dataset, divisor: int = 1):
+        assert isinstance(template_ds, xr.Dataset)
+        return {"time": int(time_len / divisor)}
+
+    kws = {} if not with_kws else {"dynamic_chunking_fn_kwargs": {"divisor": 2}}
+
+    with pipeline as p:
+        datasets = p | beam.Create(pattern.items()) | OpenWithXarray()
+        target_store = datasets | StoreToZarr(
+            target_root=tmp_target_url,
+            store_name="test.zarr",
+            combine_dims=pattern.combine_dim_keys,
+            attrs={},
+            dynamic_chunking_fn=dynamic_chunking_fn,
+            **kws,
+        )
+        open_store = target_store | OpenZarrStore()
+        assert_that(open_store, has_dynamically_set_chunks())
+
+
+def test_StoreToZarr_dynamic_chunking_with_target_chunks_raises(
+    netcdf_local_file_pattern_sequential: FilePattern,
+):
+    def fn(template_ds):
+        pass
+
+    pattern: FilePattern = netcdf_local_file_pattern_sequential
+
+    with pytest.raises(
+        ValueError,
+        match="Passing both `target_chunks` and `dynamic_chunking_fn` not allowed",
+    ):
+        _ = StoreToZarr(
+            target_root="target_root",
+            store_name="test.zarr",
+            combine_dims=pattern.combine_dim_keys,
+            target_chunks={"time": 1},
+            dynamic_chunking_fn=fn,
+        )
+
+
 def test_StoreToZarr_target_root_default_unrunnable(
     pipeline,
     netcdf_local_file_pattern_sequential,