Clear plot at beginning of loop so that non-empty image renders (#2401)

Co-authored-by: Svetlana Karslioglu <[email protected]>

Author: kiersten-stokes

Diff for: intermediate_source/mario_rl_tutorial.py

@@ -711,17 +711,18 @@ def record(self, episode, epsilon, step):
                 f"{datetime.datetime.now().strftime('%Y-%m-%dT%H:%M:%S'):>20}\n"
             )
 
-        for metric in ["ep_rewards", "ep_lengths", "ep_avg_losses", "ep_avg_qs"]:
-            plt.plot(getattr(self, f"moving_avg_{metric}"))
-            plt.savefig(getattr(self, f"{metric}_plot"))
+        for metric in ["ep_lengths", "ep_avg_losses", "ep_avg_qs", "ep_rewards"]:
             plt.clf()
+            plt.plot(getattr(self, f"moving_avg_{metric}"), label=f"moving_avg_{metric}")
+            plt.legend()
+            plt.savefig(getattr(self, f"{metric}_plot"))
 
 
 ######################################################################
 # Let’s play!
 # """""""""""""""
 #
-# In this example we run the training loop for 10 episodes, but for Mario to truly learn the ways of
+# In this example we run the training loop for 40 episodes, but for Mario to truly learn the ways of
 # his world, we suggest running the loop for at least 40,000 episodes!
 #
 use_cuda = torch.cuda.is_available()
@@ -735,7 +736,7 @@ def record(self, episode, epsilon, step):
 
 logger = MetricLogger(save_dir)
 
-episodes = 10
+episodes = 40
 for e in range(episodes):
 
     state = env.reset()