Plot without vis spec without ids_per_plot (#386)

* If not providing "ids_per_plot" it automatically assumes that "groupy_by='observable'". This should be fixed by creating the ids_per_plot based on the selected groupy by.

* Update petab/v1/visualize/plotting.py

Co-authored-by: Daniel Weindl <[email protected]>

---------

Co-authored-by: Daniel Weindl <[email protected]>

Author: PaulJonasJost

petab/v1/visualize/plotting.py

@@ -861,9 +861,15 @@ def parse_from_id_list(
         """
         if ids_per_plot is None:
             # this is the default case. If no grouping is specified,
-            # all observables are plotted. One observable per plot.
-            unique_obs_list = self._data_df[OBSERVABLE_ID].unique()
-            ids_per_plot = [[obs_id] for obs_id in unique_obs_list]
+            # each group_by category will be plotted on a separate plot
+            unique_ids_list = self._data_df[
+                {
+                    "dataset": DATASET_ID,
+                    "observable": OBSERVABLE_ID,
+                    "simulation": SIMULATION_CONDITION_ID,
+                }[group_by]
+            ].unique()
+            ids_per_plot = [[id_] for id_ in unique_ids_list]
 
         if group_by == "dataset" and DATASET_ID not in self._data_df:
             raise ValueError(