From 6a672c8088662fcc5f7ca81f0094ee532c8eaaf1 Mon Sep 17 00:00:00 2001
From: LI Yunxiang <39279048+Banmahhhh@users.noreply.github.com>
Date: Tue, 14 Jan 2020 11:23:26 +0800
Subject: [PATCH] add offline q learning (#193)

* add offline q learning

* Update README.md

* update

* yapf
---
 examples/offline-Q-learning/README.md        |  37 +++++
 examples/offline-Q-learning/atari.py         |   1 +
 examples/offline-Q-learning/atari_agent.py   | 137 +++++++++++++++++
 examples/offline-Q-learning/atari_model.py   |  50 ++++++
 examples/offline-Q-learning/atari_wrapper.py |   1 +
 examples/offline-Q-learning/dqn.py           | 111 +++++++++++++
 examples/offline-Q-learning/parallel_run.py  | 133 ++++++++++++++++
 examples/offline-Q-learning/replay_memory.py | 154 +++++++++++++++++++
 examples/offline-Q-learning/rom_files        |   1 +
 examples/offline-Q-learning/utils.py         |   1 +
 10 files changed, 626 insertions(+)
 create mode 100644 examples/offline-Q-learning/README.md
 create mode 120000 examples/offline-Q-learning/atari.py
 create mode 100644 examples/offline-Q-learning/atari_agent.py
 create mode 100644 examples/offline-Q-learning/atari_model.py
 create mode 120000 examples/offline-Q-learning/atari_wrapper.py
 create mode 100644 examples/offline-Q-learning/dqn.py
 create mode 100644 examples/offline-Q-learning/parallel_run.py
 create mode 100644 examples/offline-Q-learning/replay_memory.py
 create mode 120000 examples/offline-Q-learning/rom_files
 create mode 120000 examples/offline-Q-learning/utils.py

diff --git a/examples/offline-Q-learning/README.md b/examples/offline-Q-learning/README.md
new file mode 100644
index 0000000..f442f5d
--- /dev/null
+++ b/examples/offline-Q-learning/README.md
@@ -0,0 +1,37 @@
+## Parallel Training with PARL
+
+Use parl.compile to train the model parallelly. When applying offline training or dataset is too large to train on a single GPU, we can use parallel computing to accelerate training.
+```python
+# Set CUDA_VISIBLE_DEVICES to select which GPUs to train 
+
+import parl
+import paddle.fluid as fluid
+
+learn_program = fluid.Program()
+with fluid.program_guard(learn_program):
+    # Define your learn program and training loss
+    pass
+
+learn_program = parl.compile(learn_program, loss=training_loss)  
+# Pass the training loss to parl.compile. Distribute the model and data to GPUs.
+```
+
+## Demonstration
+
+We provide a demonstration of offline Q-learning with parallel executing, in which we seperate the procedures of collecting data and training the model. First we collect data by interacting with the environment and save them to a replay memory file, and then fit and evaluate the Q network with the collected data. Repeat these two steps to improve the performance gradually.
+
+### Dependencies:
++ [paddlepaddle>=1.5.1](https://github.com/PaddlePaddle/Paddle)
++ [parl](https://github.com/PaddlePaddle/PARL)
++ gym
++ tqdm
++ atari-py
+
+### How to Run:
+```shell
+# Collect training data
+python parallel_run.py --rom rom_files/pong.bin
+
+# Train the model offline with multi-GPU
+python parallel_run.py --rom rom_files/pong.bin --train
+```
diff --git a/examples/offline-Q-learning/atari.py b/examples/offline-Q-learning/atari.py
new file mode 120000
index 0000000..11909eb
--- /dev/null
+++ b/examples/offline-Q-learning/atari.py
@@ -0,0 +1 @@
+../DQN/atari.py
\ No newline at end of file
diff --git a/examples/offline-Q-learning/atari_agent.py b/examples/offline-Q-learning/atari_agent.py
new file mode 100644
index 0000000..abdc8b5
--- /dev/null
+++ b/examples/offline-Q-learning/atari_agent.py
@@ -0,0 +1,137 @@
+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import numpy as np
+import paddle.fluid as fluid
+import parl
+from parl import layers
+
+IMAGE_SIZE = (84, 84)
+CONTEXT_LEN = 4
+
+
+class AtariAgent(parl.Agent):
+    def __init__(self, algorithm, act_dim, total_step):
+        super(AtariAgent, self).__init__(algorithm)
+        assert isinstance(act_dim, int)
+        self.act_dim = act_dim
+        self.exploration = 1.1
+        self.global_step = 0
+        self.update_target_steps = 10000 // 4
+
+    def build_program(self):
+        self.pred_program = fluid.Program()
+        self.learn_program = fluid.Program()
+        self.supervised_eval_program = fluid.Program()
+
+        with fluid.program_guard(self.pred_program):
+            obs = layers.data(
+                name='obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            self.value = self.alg.predict(obs)
+
+        with fluid.program_guard(self.learn_program):
+            obs = layers.data(
+                name='obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            action = layers.data(name='act', shape=[1], dtype='int32')
+            reward = layers.data(name='reward', shape=[], dtype='float32')
+            next_obs = layers.data(
+                name='next_obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            terminal = layers.data(name='terminal', shape=[], dtype='bool')
+            self.cost = self.alg.learn(obs, action, reward, next_obs, terminal)
+
+        # use parl.compile to distribute data and model to GPUs
+        self.learn_program = parl.compile(self.learn_program, loss=self.cost)
+
+        with fluid.program_guard(self.supervised_eval_program):
+            obs = layers.data(
+                name='obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            action = layers.data(name='act', shape=[1], dtype='int32')
+            reward = layers.data(name='reward', shape=[], dtype='float32')
+            next_obs = layers.data(
+                name='next_obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            terminal = layers.data(name='terminal', shape=[], dtype='bool')
+            self.supervised_cost = self.alg.supervised_eval(
+                obs, action, reward, next_obs, terminal)
+
+    def sample(self, obs):
+        sample = np.random.random()
+        if sample < self.exploration:
+            act = np.random.randint(self.act_dim)
+        else:
+            if np.random.random() < 0.01:
+                act = np.random.randint(self.act_dim)
+            else:
+                obs = np.expand_dims(obs, axis=0)
+                pred_Q = self.fluid_executor.run(
+                    self.pred_program,
+                    feed={'obs': obs.astype('float32')},
+                    fetch_list=[self.value])[0]
+                pred_Q = np.squeeze(pred_Q, axis=0)
+                act = np.argmax(pred_Q)
+        self.exploration = max(0.1, self.exploration - 1e-6)
+        return act
+
+    def predict(self, obs):
+        obs = np.expand_dims(obs, axis=0)
+        pred_Q = self.fluid_executor.run(
+            self.pred_program,
+            feed={'obs': obs.astype('float32')},
+            fetch_list=[self.value])[0]
+        pred_Q = np.squeeze(pred_Q, axis=0)
+        act = np.argmax(pred_Q)
+        return act
+
+    def learn(self, obs, act, reward, next_obs, terminal):
+        if self.global_step % self.update_target_steps == 0:
+            self.alg.sync_target()
+        self.global_step += 1
+
+        act = np.expand_dims(act, -1)
+        reward = np.clip(reward, -1, 1)
+        feed = {
+            'obs': obs.astype('float32'),
+            'act': act.astype('int32'),
+            'reward': reward,
+            'next_obs': next_obs.astype('float32'),
+            'terminal': terminal
+        }
+        cost = self.fluid_executor.run(
+            self.learn_program, feed=feed, fetch_list=[self.cost])[0]
+        return cost
+
+    def supervised_eval(self, obs, act, reward, next_obs, terminal):
+        act = np.expand_dims(act, -1)
+        reward = np.clip(reward, -1, 1)
+        feed = {
+            'obs': obs.astype('float32'),
+            'act': act.astype('int32'),
+            'reward': reward,
+            'next_obs': next_obs.astype('float32'),
+            'terminal': terminal
+        }
+        cost = self.fluid_executor.run(
+            self.supervised_eval_program,
+            feed=feed,
+            fetch_list=[self.supervised_cost])[0]
+        return cost
diff --git a/examples/offline-Q-learning/atari_model.py b/examples/offline-Q-learning/atari_model.py
new file mode 100644
index 0000000..5a4bdbd
--- /dev/null
+++ b/examples/offline-Q-learning/atari_model.py
@@ -0,0 +1,50 @@
+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle.fluid as fluid
+import parl
+from parl import layers
+
+
+class AtariModel(parl.Model):
+    def __init__(self, act_dim):
+        self.act_dim = act_dim
+
+        self.conv1 = layers.conv2d(
+            num_filters=32, filter_size=5, stride=1, padding=2, act='relu')
+        self.conv2 = layers.conv2d(
+            num_filters=32, filter_size=5, stride=1, padding=2, act='relu')
+        self.conv3 = layers.conv2d(
+            num_filters=64, filter_size=4, stride=1, padding=1, act='relu')
+        self.conv4 = layers.conv2d(
+            num_filters=64, filter_size=3, stride=1, padding=1, act='relu')
+
+        self.fc1 = layers.fc(size=act_dim)
+
+    def value(self, obs):
+        obs = obs / 255.0
+        out = self.conv1(obs)
+        out = layers.pool2d(
+            input=out, pool_size=2, pool_stride=2, pool_type='max')
+        out = self.conv2(out)
+        out = layers.pool2d(
+            input=out, pool_size=2, pool_stride=2, pool_type='max')
+        out = self.conv3(out)
+        out = layers.pool2d(
+            input=out, pool_size=2, pool_stride=2, pool_type='max')
+        out = self.conv4(out)
+        out = layers.flatten(out, axis=1)
+
+        Q = self.fc1(out)
+        return Q
diff --git a/examples/offline-Q-learning/atari_wrapper.py b/examples/offline-Q-learning/atari_wrapper.py
new file mode 120000
index 0000000..e58186a
--- /dev/null
+++ b/examples/offline-Q-learning/atari_wrapper.py
@@ -0,0 +1 @@
+../DQN/atari_wrapper.py
\ No newline at end of file
diff --git a/examples/offline-Q-learning/dqn.py b/examples/offline-Q-learning/dqn.py
new file mode 100644
index 0000000..feedf7d
--- /dev/null
+++ b/examples/offline-Q-learning/dqn.py
@@ -0,0 +1,111 @@
+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import warnings
+warnings.simplefilter('default')
+
+import copy
+import paddle.fluid as fluid
+from parl.core.fluid.algorithm import Algorithm
+from parl.core.fluid import layers
+from parl.utils.deprecation import deprecated
+
+__all__ = ['DQN']
+
+
+class DQN(Algorithm):
+    def __init__(self,
+                 model,
+                 hyperparas=None,
+                 act_dim=None,
+                 gamma=None,
+                 lr=None):
+        """ DQN algorithm
+        
+        Args:
+            model (parl.Model): model defining forward network of Q function
+            hyperparas (dict): (deprecated) dict of hyper parameters.
+            act_dim (int): dimension of the action space
+            gamma (float): discounted factor for reward computation.
+            lr (float): learning rate.
+        """
+        self.model = model
+        self.target_model = copy.deepcopy(model)
+
+        if hyperparas is not None:
+            warnings.warn(
+                "the `hyperparas` argument of `__init__` function in `parl.Algorithms.DQN` is deprecated since version 1.2 and will be removed in version 1.3.",
+                DeprecationWarning,
+                stacklevel=2)
+            self.act_dim = hyperparas['action_dim']
+            self.gamma = hyperparas['gamma']
+        else:
+            assert isinstance(act_dim, int)
+            assert isinstance(gamma, float)
+            assert isinstance(lr, float)
+            self.act_dim = act_dim
+            self.gamma = gamma
+            self.lr = lr
+
+    def predict(self, obs):
+        """ use value model self.model to predict the action value
+        """
+        return self.model.value(obs)
+
+    def learn(self, obs, action, reward, next_obs, terminal):
+        """ update value model self.model with DQN algorithm
+        """
+
+        cost = self.cal_bellman_residual(obs, action, reward, next_obs,
+                                         terminal)
+        optimizer = fluid.optimizer.Adam(learning_rate=self.lr, epsilon=1e-3)
+        optimizer.minimize(cost)
+        return cost
+
+    def supervised_eval(self, obs, action, reward, next_obs, terminal):
+        """ Calculate squared Bellman residual with test dataset. The operations are the same as learn method above,
+        except backpropagation.
+        """
+        cost = self.cal_bellman_residual(obs, action, reward, next_obs,
+                                         terminal)
+        cost.stop_gradient = True
+        return cost
+
+    def cal_bellman_residual(self, obs, action, reward, next_obs, terminal):
+        """ use self.model to get squared Bellman residual with fed data
+        """
+        pred_value = self.model.value(obs)
+        next_pred_value = self.target_model.value(next_obs)
+        best_v = layers.reduce_max(next_pred_value, dim=1)
+        best_v.stop_gradient = True
+        target = reward + (
+            1.0 - layers.cast(terminal, dtype='float32')) * self.gamma * best_v
+
+        action_onehot = layers.one_hot(action, self.act_dim)
+        action_onehot = layers.cast(action_onehot, dtype='float32')
+        pred_action_value = layers.reduce_sum(
+            layers.elementwise_mul(action_onehot, pred_value), dim=1)
+        cost = layers.square_error_cost(pred_action_value, target)
+        cost = layers.reduce_mean(cost)
+        return cost
+
+    def sync_target(self, gpu_id=None):
+        """ sync weights of self.model to self.target_model
+        """
+        if gpu_id is not None:
+            warnings.warn(
+                "the `gpu_id` argument of `sync_target` function in `parl.Algorithms.DQN` is deprecated since version 1.2 and will be removed in version 1.3.",
+                DeprecationWarning,
+                stacklevel=2)
+        self.model.sync_weights_to(self.target_model)
diff --git a/examples/offline-Q-learning/parallel_run.py b/examples/offline-Q-learning/parallel_run.py
new file mode 100644
index 0000000..3416f8c
--- /dev/null
+++ b/examples/offline-Q-learning/parallel_run.py
@@ -0,0 +1,133 @@
+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import argparse
+import gym
+import numpy as np
+import os
+import time
+from tqdm import tqdm
+
+import parl
+import paddle.fluid as fluid
+from parl.utils import get_gpu_count
+from parl.utils import tensorboard, logger
+
+from dqn import DQN  # slight changes from parl.algorithms.DQN
+from atari_agent import AtariAgent
+from atari_model import AtariModel
+from replay_memory import ReplayMemory, Experience
+from utils import get_player
+
+MEMORY_SIZE = int(1e6)
+MEMORY_WARMUP_SIZE = MEMORY_SIZE // 20
+IMAGE_SIZE = (84, 84)
+CONTEXT_LEN = 4
+FRAME_SKIP = 4
+UPDATE_FREQ = 4
+GAMMA = 0.99
+LEARNING_RATE = 3e-4
+
+gpu_num = get_gpu_count()
+
+
+def run_train_step(agent, rpm):
+    for step in range(args.train_total_steps):
+        # use the first 80% data to train
+        batch_all_state, batch_action, batch_reward, batch_isOver = rpm.sample_batch(
+            args.batch_size * gpu_num)
+        batch_state = batch_all_state[:, :CONTEXT_LEN, :, :]
+        batch_next_state = batch_all_state[:, 1:, :, :]
+        cost = agent.learn(batch_state, batch_action, batch_reward,
+                           batch_next_state, batch_isOver)
+
+        if step % 100 == 0:
+            # use the last 20% data to evaluate
+            batch_all_state, batch_action, batch_reward, batch_isOver = rpm.sample_test_batch(
+                args.batch_size)
+            batch_state = batch_all_state[:, :CONTEXT_LEN, :, :]
+            batch_next_state = batch_all_state[:, 1:, :, :]
+            eval_cost = agent.supervised_eval(batch_state, batch_action,
+                                              batch_reward, batch_next_state,
+                                              batch_isOver)
+            logger.info(
+                "train step {}, train costs are {}, eval cost is {}.".format(
+                    step, cost, eval_cost))
+
+
+def collect_exp(env, rpm, agent):
+    state = env.reset()
+    # collect data to fulfill replay memory
+    for i in tqdm(range(MEMORY_SIZE)):
+        context = rpm.recent_state()
+        context.append(state)
+        context = np.stack(context, axis=0)
+        action = agent.sample(context)
+
+        next_state, reward, isOver, _ = env.step(action)
+        rpm.append(Experience(state, action, reward, isOver))
+        state = next_state
+
+
+def main():
+    env = get_player(
+        args.rom, image_size=IMAGE_SIZE, train=True, frame_skip=FRAME_SKIP)
+    file_path = "memory.npz"
+    rpm = ReplayMemory(
+        MEMORY_SIZE,
+        IMAGE_SIZE,
+        CONTEXT_LEN,
+        load_file=True,  # load replay memory data from file
+        file_path=file_path)
+    act_dim = env.action_space.n
+
+    model = AtariModel(act_dim)
+    algorithm = DQN(
+        model, act_dim=act_dim, gamma=GAMMA, lr=LEARNING_RATE * gpu_num)
+    agent = AtariAgent(
+        algorithm, act_dim=act_dim, total_step=args.train_total_steps)
+    if os.path.isfile('./model.ckpt'):
+        logger.info("load model from file")
+        agent.restore('./model.ckpt')
+
+    if args.train:
+        logger.info("train with memory data")
+        run_train_step(agent, rpm)
+        logger.info("finish training. Save the model.")
+        agent.save('./model.ckpt')
+    else:
+        logger.info("collect experience")
+        collect_exp(env, rpm, agent)
+        rpm.save_memory()
+        logger.info("finish collecting, save successfully")
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        '--rom', help='path of the rom of the atari game', required=True)
+    parser.add_argument(
+        '--batch_size', type=int, default=64, help='batch size for each GPU')
+    parser.add_argument(
+        '--train',
+        action="store_true",
+        help='update the value function (default: False)')
+    parser.add_argument(
+        '--train_total_steps',
+        type=int,
+        default=int(1e6),
+        help='maximum environmental steps of games')
+
+    args = parser.parse_args()
+    main()
diff --git a/examples/offline-Q-learning/replay_memory.py b/examples/offline-Q-learning/replay_memory.py
new file mode 100644
index 0000000..2296ea9
--- /dev/null
+++ b/examples/offline-Q-learning/replay_memory.py
@@ -0,0 +1,154 @@
+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import numpy as np
+import copy
+import os
+from collections import deque, namedtuple
+from parl.utils import logger
+
+Experience = namedtuple('Experience', ['state', 'action', 'reward', 'isOver'])
+
+
+class ReplayMemory(object):
+    def __init__(self,
+                 max_size,
+                 state_shape,
+                 context_len,
+                 load_file=False,
+                 file_path=None):
+        self.max_size = int(max_size)
+        self.state_shape = state_shape
+        self.context_len = int(context_len)
+
+        self.file_path = file_path
+        if load_file and os.path.isfile(file_path):
+            logger.info("load memory from file" + self.file_path)
+            self.load_memory()
+            logger.info("memory size is {}".format(self._curr_size))
+        else:
+            self.state = np.zeros(
+                (self.max_size, ) + state_shape, dtype='uint8')
+            self.action = np.zeros((self.max_size, ), dtype='int32')
+            self.reward = np.zeros((self.max_size, ), dtype='float32')
+            self.isOver = np.zeros((self.max_size, ), dtype='bool')
+
+            self._curr_size = 0
+            self._curr_pos = 0
+            self._context = deque(maxlen=context_len - 1)
+
+    def append(self, exp):
+        """append a new experience into replay memory
+        """
+        if self._curr_size < self.max_size:
+            self._assign(self._curr_pos, exp)
+            self._curr_size += 1
+        else:
+            self._assign(self._curr_pos, exp)
+        self._curr_pos = (self._curr_pos + 1) % self.max_size
+        if exp.isOver:
+            self._context.clear()
+        else:
+            self._context.append(exp)
+
+    def recent_state(self):
+        """ maintain recent state for training"""
+        lst = list(self._context)
+        states = [np.zeros(self.state_shape, dtype='uint8')] * \
+                    (self._context.maxlen - len(lst))
+        states.extend([k.state for k in lst])
+        return states
+
+    def sample(self, idx):
+        """ return state, action, reward, isOver,
+            note that some frames in state may be generated from last episode,
+            they should be removed from state
+            """
+        state = np.zeros(
+            (self.context_len + 1, ) + self.state_shape, dtype=np.uint8)
+        state_idx = np.arange(idx,
+                              idx + self.context_len + 1) % self._curr_size
+
+        # confirm that no frame was generated from last episode
+        has_last_episode = False
+        for k in range(self.context_len - 2, -1, -1):
+            to_check_idx = state_idx[k]
+            if self.isOver[to_check_idx]:
+                has_last_episode = True
+                state_idx = state_idx[k + 1:]
+                state[k + 1:] = self.state[state_idx]
+                break
+
+        if not has_last_episode:
+            state = self.state[state_idx]
+
+        real_idx = (idx + self.context_len - 1) % self._curr_size
+        action = self.action[real_idx]
+        reward = self.reward[real_idx]
+        isOver = self.isOver[real_idx]
+        return state, reward, action, isOver
+
+    def __len__(self):
+        return self._curr_size
+
+    def size(self):
+        return self._curr_size
+
+    def _assign(self, pos, exp):
+        self.state[pos] = exp.state
+        self.reward[pos] = exp.reward
+        self.action[pos] = exp.action
+        self.isOver[pos] = exp.isOver
+
+    def sample_batch(self, batch_size):
+        """sample a batch from replay memory for training
+        """
+        batch_idx = np.random.randint(
+            int(self.max_size * 0.8) - self.context_len - 1, size=batch_size)
+        # batch_idx = (self._curr_pos + batch_idx) % self._curr_size
+        batch_exp = [self.sample(i) for i in batch_idx]
+        return self._process_batch(batch_exp)
+
+    def sample_test_batch(self, batch_size):
+        batch_idx = np.random.randint(
+            int(self.max_size * 0.2) - self.context_len - 1,
+            size=batch_size) + int(self.max_size * 0.8)
+        # batch_idx = (self._curr_pos + batch_idx) % self._curr_size
+        batch_exp = [self.sample(i) for i in batch_idx]
+        return self._process_batch(batch_exp)
+
+    def _process_batch(self, batch_exp):
+        state = np.asarray([e[0] for e in batch_exp], dtype='uint8')
+        reward = np.asarray([e[1] for e in batch_exp], dtype='float32')
+        action = np.asarray([e[2] for e in batch_exp], dtype='int8')
+        isOver = np.asarray([e[3] for e in batch_exp], dtype='bool')
+        return [state, action, reward, isOver]
+
+    def save_memory(self):
+        save_data = [
+            self.state, self.reward, self.action, self.isOver, self._curr_size,
+            self._curr_pos, self._context
+        ]
+        np.savez(self.file_path, *save_data)
+
+    def load_memory(self):
+        container = np.load(self.file_path, allow_pickle=True)
+        [
+            self.state, self.reward, self.action, self.isOver, self._curr_size,
+            self._curr_pos, self._context
+        ] = [container[key] for key in container]
+        self._curr_size = self._curr_size.astype(int)
+        self._curr_pos = self._curr_pos.astype(int)
+        self._context = deque([Experience(*row) for row in self._context],
+                              maxlen=self.context_len - 1)
diff --git a/examples/offline-Q-learning/rom_files b/examples/offline-Q-learning/rom_files
new file mode 120000
index 0000000..966a894
--- /dev/null
+++ b/examples/offline-Q-learning/rom_files
@@ -0,0 +1 @@
+../DQN/rom_files/
\ No newline at end of file
diff --git a/examples/offline-Q-learning/utils.py b/examples/offline-Q-learning/utils.py
new file mode 120000
index 0000000..721338d
--- /dev/null
+++ b/examples/offline-Q-learning/utils.py
@@ -0,0 +1 @@
+../DQN/utils.py
\ No newline at end of file
-- 
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