Added a way to cap the number of demonstrations that are kept in the buffer

rltorch/memory/DQfDMemory.py

@@ -7,9 +7,11 @@ Transition = namedtuple('Transition',
 
 
 class DQfDMemory(PrioritizedReplayMemory):
-    def __init__(self, capacity, alpha):
+    def __init__(self, capacity, alpha, max_demo = -1):
+        assert max_demo <= capacity
         super().__init__(capacity, alpha)
         self.demo_position = 0
+        self.max_demo = max_demo # -1 means no maximum number of demonstrations
     
     def append(self, *args, **kwargs):
         last_position = self.position # Get position before super classes change it
@@ -21,7 +23,8 @@ class DQfDMemory(PrioritizedReplayMemory):
     def append_demonstration(self, *args):
         demonstrations = self.memory[:self.demo_position]
         obtained_transitions = self.memory[self.demo_position:]
-        if len(demonstrations) + 1 > self.capacity:
+        max_demo = self.max_demo if self.max_demo > -1 else self.capacity
+        if len(demonstrations) + 1 > max_demo:
             self.memory.pop(0)
             self.memory.append(Transition(*args))
         else: