Add spatial presence matrices and use in ExperimentAxisQuery

This adds dataframes for creating a join table between the scenes and
observations/variables. New methods are added to the
`ExperimentAxisQuery` class for getting a Arrow array of scene names
that relate to the obs or var in the query.

python-spec/src/somacore/experiment.py

@@ -66,6 +66,17 @@ class Experiment(
     spatial = _mixin.item[_SceneColl]()  # TODO: Discuss the name of this element.
     """A collection of named spatial scenes."""
 
+    obs_spatial_presence = _mixin.item[_DF]()
+    """A dataframe that stores the presence of obs in the spatial scenes.
+
+    This provides a join table for the obs ``soma_joinid`` and the scene names used in
+    the ``spatial`` collection. This dataframe must contain dimensions ``soma_joinid``
+    and ``scene_id``. The ``scene_id`` dimension must be a ``string`` dimension. The
+    dataframe must contain a ``boolean`` column ``data``. The values of ``data`` are
+    ``True`` if the obs with obsid ``soma_joinid`` is contained in the scene
+    ``scene_id`` and ``False`` otherwise.
+    """
+
     def axis_query(
         self,
         measurement_name: str,

python-spec/src/somacore/measurement.py

@@ -99,3 +99,14 @@ class Measurement(
 
     This is indexed by ``[varid_1, varid_2]``.
     """
+
+    var_spatial_presence = _mixin.item[_DF]()
+    """A dataframe that stores the presence of var in the spatial scenes.
+
+    This provides a join tabel for the var ``soma_joinid`` and the scene names used in
+    the ``spatial`` collection. This dataframe must contain dimensions ``soma_joinid``
+    and ``scene_id``. The ``scene_id`` dimension must be a ``string`` dimension. The
+    dataframe must contain a ``boolean`` column ``data``. The values of ``data`` are
+    ``True`` if the var with varid ``soma_joinid`` is contained in scene with name
+    ``scene_id`` and ``False`` otherwise.
+    """

python-spec/src/somacore/query/query.py

@@ -21,6 +21,7 @@
 import numpy.typing as npt
 import pandas as pd
 import pyarrow as pa
+import pyarrow.compute as pacomp
 from scipy import sparse
 from typing_extensions import Literal, Protocol, Self, TypedDict
 
@@ -267,6 +268,48 @@ def varm(self, layer: str) -> data.SparseRead:
         """
         return self._axism_inner(_Axis.VAR, layer)
 
+    def obs_scene_ids(self) -> pa.Array:
+        """Returns a pyarrow array with scene ids that contain obs from this
+        query.
+
+        Lifecycle: experimental
+        """
+        try:
+            obs_scene = self.experiment.obs_spatial_presence
+        except KeyError as ke:
+            raise KeyError("Missing obs_scene") from ke
+        if not isinstance(obs_scene, data.DataFrame):
+            raise TypeError("obs_scene must be a dataframe.")
+
+        full_table = obs_scene.read(
+            coords=((_Axis.OBS.getattr_from(self._joinids), slice(None))),
+            result_order=options.ResultOrder.COLUMN_MAJOR,
+            value_filter="data != 0",
+        ).concat()
+
+        return pacomp.unique(full_table["scene_id"])
+
+    def var_scene_ids(self) -> pa.Array:
+        """Return a pyarrow array with scene ids that contain var from this
+        query.
+
+        Lifecycle: experimental
+        """
+        try:
+            var_scene = self._ms.var_spatial_presence
+        except KeyError as ke:
+            raise KeyError("Missing var_scene") from ke
+        if not isinstance(var_scene, data.DataFrame):
+            raise TypeError("var_scene must be a dataframe.")
+
+        full_table = var_scene.read(
+            coords=((_Axis.OBS.getattr_from(self._joinids), slice(None))),
+            result_order=options.ResultOrder.COLUMN_MAJOR,
+            value_filter="data != 0",
+        ).concat()
+
+        return pacomp.unique(full_table["scene_id"])
+
     def to_anndata(
         self,
         X_name: str,
@@ -827,6 +870,9 @@ def obs(self) -> data.DataFrame: ...
     @property
     def context(self) -> Optional[base_types.ContextBase]: ...
 
+    @property
+    def obs_spatial_presence(self) -> data.DataFrame: ...
+
 
 class _HasObsVar(Protocol[_T_co]):
     """Something which has an ``obs`` and ``var`` field.