Add Collection.from_items

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- `Collection.from_items` for creating a `pystac.Collection` from an `ItemCollection` ([#1522](https://github.com/stac-utils/pystac/pull/1522))
+
 ### Fixed
 
 - Make sure that `VersionRange` has `VersionID`s rather than strings ([#1512](https://github.com/stac-utils/pystac/pull/1512))

docs/api/pystac.rst

@@ -141,6 +141,7 @@ ItemCollection
 .. autoclass:: pystac.ItemCollection
    :members:
    :inherited-members:
+   :undoc-members:
 
 Link
 ----

pystac/collection.py

@@ -710,6 +710,77 @@ def from_dict(
 
         return collection
 
+    @classmethod
+    def from_items(
+        cls: type[Collection],
+        items: Iterable[Item] | pystac.ItemCollection,
+        *,
+        id: str | None = None,
+        strategy: HrefLayoutStrategy | None = None,
+    ) -> Collection:
+        """Create a :class:`Collection` from iterable of items or an
+        :class:`~pystac.ItemCollection`.
+
+        Will try to pull collection attributes from
+        :attr:`~pystac.ItemCollection.extra_fields` and items when possible.
+
+        Args:
+            items : Iterable of :class:`~pystac.Item` instances to include in the
+                :class:`Collection`. This can be a :class:`~pystac.ItemCollection`.
+            id : Identifier for the collection. If not set, must be available on the
+                items and they must all match.
+            strategy : The layout strategy to use for setting the
+                HREFs of the catalog child objections and items.
+                If not provided, it will default to strategy of the parent and fallback
+                to :class:`~pystac.layout.BestPracticesLayoutStrategy`.
+        """
+
+        def extract(attr: str) -> Any:
+            """Extract attrs from items or item.properties as long as they all match"""
+            value = None
+            values = {getattr(item, attr, None) for item in items}
+            if len(values) == 1:
+                value = next(iter(values))
+                if value is None:
+                    values = {item.properties.get(attr, None) for item in items}
+                    if len(values) == 1:
+                        value = next(iter(values))
+            return value
+
+        if isinstance(items, pystac.ItemCollection):
+            extra_fields = deepcopy(items.extra_fields)
+            links = extra_fields.pop("links", {})
+            providers = extra_fields.pop("providers", None)
+            if providers is not None:
+                providers = [pystac.Provider.from_dict(p) for p in providers]
+        else:
+            extra_fields = {}
+            links = {}
+            providers = []
+
+        id = id or extract("collection_id")
+        if id is None:
+            raise ValueError(
+                "Collection id must be defined. Either by specifying collection_id "
+                "on every item, or as a keyword argument to this function."
+            )
+
+        collection = cls(
+            id=id,
+            description=extract("description"),
+            extent=Extent.from_items(items),
+            title=extract("title"),
+            providers=providers,
+            extra_fields=extra_fields,
+            strategy=strategy,
+        )
+        collection.add_items(items)
+
+        for link in links:
+            collection.add_link(Link.from_dict(link))
+
+        return collection
+
     def get_item(self, id: str, recursive: bool = False) -> Item | None:
         """Returns an item with a given ID.
 

tests/conftest.py

@@ -9,7 +9,7 @@
 
 import pytest
 
-from pystac import Asset, Catalog, Collection, Item, Link
+from pystac import Asset, Catalog, Collection, Item, ItemCollection, Link
 
 from .utils import ARBITRARY_BBOX, ARBITRARY_EXTENT, ARBITRARY_GEOM, TestCases
 
@@ -76,6 +76,18 @@ def sample_item() -> Item:
     return Item.from_file(TestCases.get_path("data-files/item/sample-item.json"))
 
 
+@pytest.fixture
+def sample_item_collection() -> ItemCollection:
+    return ItemCollection.from_file(
+        TestCases.get_path("data-files/item-collection/sample-item-collection.json")
+    )
+
+
+@pytest.fixture
+def sample_items(sample_item_collection: ItemCollection) -> list[Item]:
+    return list(sample_item_collection)
+
+
 @pytest.fixture(scope="function")
 def tmp_asset(tmp_path: Path) -> Asset:
     """Copy the entirety of test-case-2 to tmp and"""

tests/test_collection.py

@@ -19,6 +19,7 @@
     Collection,
     Extent,
     Item,
+    ItemCollection,
     Provider,
     SpatialExtent,
     TemporalExtent,
@@ -711,3 +712,111 @@ def test_permissive_temporal_extent_deserialization(collection: Collection) -> N
     ]["interval"][0]
     with pytest.warns(UserWarning):
         Collection.from_dict(collection_dict)
+
+
+@pytest.mark.parametrize("fixture_name", ("sample_item_collection", "sample_items"))
+def test_from_items(fixture_name: str, request: pytest.FixtureRequest) -> None:
+    items = request.getfixturevalue(fixture_name)
+    collection = Collection.from_items(items)
+
+    for item in items:
+        assert collection.id == item.collection_id
+        assert collection.extent.spatial.bboxes[0][0] <= item.bbox[0]
+        assert collection.extent.spatial.bboxes[0][1] <= item.bbox[1]
+        assert collection.extent.spatial.bboxes[0][2] >= item.bbox[2]
+        assert collection.extent.spatial.bboxes[0][3] >= item.bbox[3]
+
+        start = collection.extent.temporal.intervals[0][0]
+        end = collection.extent.temporal.intervals[0][1]
+        assert start and start <= str_to_datetime(item.properties["start_datetime"])
+        assert end and end >= str_to_datetime(item.properties["end_datetime"])
+
+    if isinstance(items, ItemCollection):
+        expected = {(link["rel"], link["href"]) for link in items.extra_fields["links"]}
+        actual = {(link.rel, link.href) for link in collection.links}
+        assert expected.issubset(actual)
+
+
+def test_from_items_pulls_from_properties() -> None:
+    item1 = Item(
+        id="test-item-1",
+        geometry=ARBITRARY_GEOM,
+        bbox=[-10, -20, 0, -10],
+        datetime=datetime(2000, 2, 1, 12, 0, 0, 0, tzinfo=tz.UTC),
+        collection="test-collection-1",
+        properties={"title": "Test Item", "description": "Extra words describing"},
+    )
+    collection = Collection.from_items([item1])
+    assert collection.id == item1.collection_id
+    assert collection.title == item1.properties["title"]
+    assert collection.description == item1.properties["description"]
+
+
+def test_from_items_without_collection_id() -> None:
+    item1 = Item(
+        id="test-item-1",
+        geometry=ARBITRARY_GEOM,
+        bbox=[-10, -20, 0, -10],
+        datetime=datetime(2000, 2, 1, 12, 0, 0, 0, tzinfo=tz.UTC),
+        properties={},
+    )
+    with pytest.raises(ValueError, match="Collection id must be defined."):
+        Collection.from_items([item1])
+
+    collection = Collection.from_items([item1], id="test-collection")
+    assert collection.id == "test-collection"
+
+
+def test_from_items_with_collection_ids() -> None:
+    item1 = Item(
+        id="test-item-1",
+        geometry=ARBITRARY_GEOM,
+        bbox=[-10, -20, 0, -10],
+        datetime=datetime(2000, 2, 1, 12, 0, 0, 0, tzinfo=tz.UTC),
+        collection="test-collection-1",
+        properties={},
+    )
+    item2 = Item(
+        id="test-item-2",
+        geometry=ARBITRARY_GEOM,
+        bbox=[-15, -20, 0, -10],
+        datetime=datetime(2000, 2, 1, 13, 0, 0, 0, tzinfo=tz.UTC),
+        collection="test-collection-2",
+        properties={},
+    )
+
+    with pytest.raises(ValueError, match="Collection id must be defined."):
+        Collection.from_items([item1, item2])
+
+    collection = Collection.from_items([item1, item2], id="test-collection")
+    assert collection.id == "test-collection"
+
+
+def test_from_items_with_different_values() -> None:
+    item1 = Item(
+        id="test-item-1",
+        geometry=ARBITRARY_GEOM,
+        bbox=[-10, -20, 0, -10],
+        datetime=datetime(2000, 2, 1, 12, 0, 0, 0, tzinfo=tz.UTC),
+        properties={"title": "Test Item 1"},
+    )
+    item2 = Item(
+        id="test-item-2",
+        geometry=ARBITRARY_GEOM,
+        bbox=[-15, -20, 0, -10],
+        datetime=datetime(2000, 2, 1, 13, 0, 0, 0, tzinfo=tz.UTC),
+        properties={"title": "Test Item 2"},
+    )
+
+    collection = Collection.from_items([item1, item2], id="test_collection")
+    assert collection.title is None
+
+
+def test_from_items_with_providers(sample_item_collection: ItemCollection) -> None:
+    sample_item_collection.extra_fields["providers"] = [{"name": "pystac"}]
+
+    collection = Collection.from_items(sample_item_collection)
+    assert collection.providers and len(collection.providers) == 1
+
+    provider = collection.providers[0]
+    assert provider and provider.name == "pystac"