fix(pm4py): minor fix OCEL interleavings computation

Author: fit-alessandro-berti

pm4py/objects/ocel/util/log_ocel.py

@@ -125,6 +125,7 @@ def __get_events_dataframe(df: pd.DataFrame, activity_key: str, timestamp_key: s
     Internal method to get the events dataframe out of a traditional log stored as Pandas dataframe
     """
     columns = {case_id_key}.union(set(x for x in df.columns if not x.startswith(case_attribute_prefix)))
+    columns = list(columns)
     df = df[columns]
     df = df.rename(columns={activity_key: ocel_constants.DEFAULT_EVENT_ACTIVITY,
                             timestamp_key: ocel_constants.DEFAULT_EVENT_TIMESTAMP,
@@ -139,6 +140,7 @@ def __get_objects_dataframe(df: pd.DataFrame, case_id_key: str, case_attribute_p
     Internal method to get the objects dataframe out of a traditional log stored as Pandas dataframe
     """
     columns = {x for x in df.columns if x.startswith(case_attribute_prefix)}
+    columns = list(columns)
     df = df[columns]
     df = df.rename(columns={case_id_key: ocel_constants.DEFAULT_OBJECT_ID})
     df = df.groupby(ocel_constants.DEFAULT_OBJECT_ID).first().reset_index()