minor fix for specifying the element (#51)

Author: giovp

src/spatialdata_plot/pl/basic.py

@@ -508,7 +508,7 @@ def show(
 
         # check that coordinate system and elements to be rendered match
         for cmd, params in render_cmds.items():
-            if params.element is not None and len(params.element) != len(coordinate_system):
+            if params.element is not None and len([params.element]) != len(coordinate_system):
                 raise ValueError(
                     f"Number of coordinate systems ({len(coordinate_system)}) does not match number of elements "
                     f"({len(params.element)}) in command {cmd}."

src/spatialdata_plot/pl/render.py

@@ -106,9 +106,9 @@ def _get_collection_shape(
         **kwargs: Any,
     ) -> PatchCollection:
         """Get collection of shapes."""
-        if shapes["geometry"][0].geom_type == "Polygon":
+        if shapes["geometry"].iloc[0].geom_type == "Polygon":
             patches = [Polygon(p.exterior.coords, closed=False) for p in shapes["geometry"]]
-        elif shapes["geometry"][0].geom_type == "Point":
+        elif shapes["geometry"].iloc[0].geom_type == "Point":
             patches = [Circle((circ.x, circ.y), radius=r * s) for circ, r in zip(shapes["geometry"], shapes["radius"])]
 
         collection = PatchCollection(patches, snap=False, **kwargs)