fix obs_vector / var_vector return type

(cherry picked from commit 8f195de)

Author: ilia-kats

CHANGELOG.md

@@ -17,6 +17,13 @@ and this project adheres to [Semantic Versioning][].
 - The settings API has changed. Use e.g. `mudata.settings.pull_on_update = True` instead of `mudata.set_options(pull_on_update=True)` and use
   `mudata.settings.override` as context manager for local settings overrides.
 
+## [0.3.8] (Unreleased)
+
+### Fixed
+
+- `obs_vector` and `var_vector` once again return Pandas Series objects when appropriate. This fixes
+  applying `sc.pl.umap` on a MuData object.
+
 ## [0.3.7]
 
 ### Fixed
@@ -172,6 +179,7 @@ To copy the annotations explicitly, you will need to use `pull_obs()` and/or `pu
 Initial `mudata` release with `MuData`, previously a part of the `muon` framework.
 
 [0.4.0]: https://github.com/scverse/mudata/releases/tag/v0.4.0
+[0.3.8]: https://github.com/scverse/mudata/releases/tag/v0.3.8
 [0.3.7]: https://github.com/scverse/mudata/releases/tag/v0.3.7
 [0.3.6]: https://github.com/scverse/mudata/releases/tag/v0.3.6
 [0.3.5]: https://github.com/scverse/mudata/releases/tag/v0.3.5

src/mudata/_core/mudata.py

@@ -820,7 +820,7 @@ def _attr_vector(self, key: str, attr: str) -> np.ndarray:
                         f"There is no key {key} in MuData .{attr} but there is one in {m} .{attr}. Consider running `update_{attr}()` to update global .{attr}."
                     )
             raise KeyError(f"There is no key {key} in MuData .{attr} or in .{attr} of any modalities.")
-        return df[key].to_numpy()
+        return df[key].values
 
     @deprecated(Deprecation("0.3.4"))
     def obs_vector(self, key: str, layer: str | None = None) -> np.ndarray: