fixed bug in generator related to random sampling

flatland/envs/schedule_generators.py

@@ -87,13 +87,18 @@ def sparse_schedule_generator(speed_ratio_map: Mapping[float, float] = None, see
             # Set target for agent
             start_city = agent_start_targets_cities[agent_idx][0]
             target_city = agent_start_targets_cities[agent_idx][1]
-            start = np.random.choice(train_stations[start_city])
-            target = np.random.choice(train_stations[target_city])
+
+            start_idx = np.random.choice(np.arange(len(train_stations[start_city])))
+            target_idx = np.random.choice(np.arange(len(train_stations[target_city])))
+            start = train_stations[start_city][start_idx]
+            target = train_stations[target_city][target_idx]
 
             while start[1] % 2 != 0:
-                start = np.random.choice(train_stations[start_city])
+                start_idx = np.random.choice(np.arange(len(train_stations[start_city])))
+                start = train_stations[start_city][start_idx]
             while target[1] % 2 != 1:
-                target = np.random.choice(train_stations[target_city])
+                target_idx = np.random.choice(np.arange(len(train_stations[target_city])))
+                target = train_stations[target_city][target_idx]
             agent_orientation = (agent_start_targets_cities[agent_idx][2] + 2 * start[1]) % 4
             if not rail.check_path_exists(start[0], agent_orientation, target[0]):
                 agent_orientation = (agent_orientation + 2) % 4

tests/test_random_seeding.py

@@ -20,7 +20,7 @@ def test_random_seeding():
         # Test generation print
 
         env.agents[0].target = (0, 0)
-        for step in range(100):
+        for step in range(10):
             actions = {}
             actions[0] = 2
             env.step(actions)