simplify: eliminate duplicate set_index, vectorize astype, use list.append

- Pass pre-built cs_index to _get_elements_to_be_rendered instead of
  rebuilding set_index("cs") inside the function
- Vectorize astype("bool") to a single assignment over content_flags
- Replace += [elem] with .append(elem) in render cmd loop

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: timtreis

src/spatialdata_plot/pl/basic.py

@@ -1057,7 +1057,7 @@ def show(
         cs_index = cs_contents.set_index("cs")
         pending_colorbars: list[tuple[Axes, list[ColorbarSpec]]] = []
 
-        elements_to_be_rendered = _get_elements_to_be_rendered(render_cmds, cs_contents, cs)
+        elements_to_be_rendered = _get_elements_to_be_rendered(render_cmds, cs_index, cs)
 
         # filter out cs without relevant elements
         cmds = [cmd for cmd, _ in render_cmds]

src/spatialdata_plot/pl/utils.py

@@ -348,8 +348,7 @@ def _get_cs_contents(sdata: sd.SpatialData) -> pd.DataFrame:
         )
 
     cs_contents = pd.DataFrame(rows, columns=["cs"] + content_flags)
-    for flag in content_flags:
-        cs_contents[flag] = cs_contents[flag].astype("bool")
+    cs_contents[content_flags] = cs_contents[content_flags].astype("bool")
     return cs_contents
 
 
@@ -2093,7 +2092,7 @@ def _get_elements_to_be_rendered(
             ImageRenderParams | LabelsRenderParams | PointsRenderParams | ShapesRenderParams,
         ]
     ],
-    cs_contents: pd.DataFrame,
+    cs_index: pd.DataFrame,
     cs: str,
 ) -> list[str]:
     """
@@ -2103,24 +2102,23 @@ def _get_elements_to_be_rendered(
     ----------
     render_cmds
         List of tuples containing the commands and their respective parameters.
-    cs_contents
-        The dataframe indicating for each coordinate system which SpatialElements it contains.
+    cs_index
+        The cs_contents dataframe indexed by the "cs" column.
     cs
-        The name of the coordinate system to query cs_contents for.
+        The name of the coordinate system to query cs_index for.
 
     Returns
     -------
     List of names of the SpatialElements to be rendered in the plot.
     """
     elements_to_be_rendered: list[str] = []
 
-    cs_index = cs_contents.set_index("cs")
     cs_row = cs_index.loc[cs] if cs in cs_index.index else None
 
     for cmd, params in render_cmds:
         key = _RENDER_CMD_TO_CS_FLAG.get(cmd)
         if key and cs_row is not None and cs_row[key]:
-            elements_to_be_rendered += [params.element]
+            elements_to_be_rendered.append(params.element)
 
     return elements_to_be_rendered