[RLlib] Cleanup examples folder 18: Add example script for offline RL (BC) training on single-agent, while evaluating w/ multi-agent setup.

rllib/BUILD

@@ -3021,6 +3021,17 @@ py_test(
 
 # subdirectory: offline_rl/
 # ....................................
+
+# @HybridAPIStack
+py_test(
+    name = "examples/offline_rl/pretrain_bc_single_agent_evaluate_as_multi_agent",
+    main = "examples/offline_rl/pretrain_bc_single_agent_evaluate_as_multi_agent.py",
+    tags = ["team:rllib", "exclusive", "examples"],
+    size = "large",
+    srcs = ["examples/offline_rl/pretrain_bc_single_agent_evaluate_as_multi_agent.py"],
+    args = ["--as-test"]
+)
+
 #@OldAPIStack
 # TODO (sven): Doesn't seem to learn at the moment. Uncomment once fixed.
 # py_test(

rllib/algorithms/algorithm.py

@@ -1121,9 +1121,8 @@ def _evaluate_with_custom_eval_function(self):
     def _evaluate_on_local_env_runner(self, env_runner):
         if hasattr(env_runner, "input_reader") and env_runner.input_reader is None:
             raise ValueError(
-                "Cannot evaluate on a local worker (wether there is no evaluation "
-                "EnvRunnerGroup OR no remote evaluation workers) in the Algorithm or "
-                "w/o an environment on that local worker!\nTry one of the following:"
+                "Can't evaluate on a local worker if this local worker does not have "
+                "an environment!\nTry one of the following:"
                 "\n1) Set `evaluation_interval` > 0 to force creating a separate "
                 "evaluation EnvRunnerGroup.\n2) Set `create_env_on_driver=True` to "
                 "force the local (non-eval) EnvRunner to have an environment to "

rllib/algorithms/bc/bc.py

@@ -9,7 +9,9 @@
 from ray.rllib.utils.metrics import (
     ALL_MODULES,
     NUM_AGENT_STEPS_SAMPLED,
+    NUM_AGENT_STEPS_TRAINED,
     NUM_ENV_STEPS_SAMPLED,
+    NUM_ENV_STEPS_TRAINED,
     SAMPLE_TIMER,
     SYNCH_WORKER_WEIGHTS_TIMER,
 )
@@ -166,34 +168,51 @@ def training_step(self) -> ResultDict:
                         max_env_steps=self.config.train_batch_size,
                     )
 
-                train_batch = train_batch.as_multi_agent()
-                self._counters[NUM_AGENT_STEPS_SAMPLED] += train_batch.agent_steps()
-                self._counters[NUM_ENV_STEPS_SAMPLED] += train_batch.env_steps()
+                # TODO (sven): Use metrics API as soon as we moved to new API stack
+                #  (from currently hybrid stack).
+                # self.metrics.log_dict(
+                #    {
+                #        NUM_AGENT_STEPS_SAMPLED_LIFETIME: len(train_batch),
+                #        NUM_ENV_STEPS_SAMPLED_LIFETIME: len(train_batch),
+                #    },
+                #    reduce="sum",
+                # )
+                self._counters[NUM_AGENT_STEPS_SAMPLED] += len(train_batch)
+                self._counters[NUM_ENV_STEPS_SAMPLED] += len(train_batch)
 
             # Updating the policy.
             train_results = self.learner_group.update_from_batch(batch=train_batch)
+            # TODO (sven): Use metrics API as soon as we moved to new API stack
+            #  (from currently hybrid stack).
+            # self.metrics.log_dict(
+            #    {
+            #        NUM_AGENT_STEPS_TRAINED_LIFETIME: len(train_batch),
+            #        NUM_ENV_STEPS_TRAINED_LIFETIME: len(train_batch),
+            #    },
+            #    reduce="sum",
+            # )
+            self._counters[NUM_AGENT_STEPS_TRAINED] += len(train_batch)
+            self._counters[NUM_ENV_STEPS_TRAINED] += len(train_batch)
 
             # Synchronize weights.
             # As the results contain for each policy the loss and in addition the
             # total loss over all policies is returned, this total loss has to be
             # removed.
             policies_to_update = set(train_results.keys()) - {ALL_MODULES}
 
-            global_vars = {
-                "timestep": self._counters[NUM_AGENT_STEPS_SAMPLED],
-            }
-
+            # with self.metrics.log_time((TIMERS, SYNCH_WORKER_WEIGHTS_TIMER)):
             with self._timers[SYNCH_WORKER_WEIGHTS_TIMER]:
                 if self.workers.num_remote_workers() > 0:
                     self.workers.sync_weights(
                         from_worker_or_learner_group=self.learner_group,
                         policies=policies_to_update,
-                        global_vars=global_vars,
                     )
                 # Get weights from Learner to local worker.
                 else:
                     self.workers.local_worker().set_weights(
                         self.learner_group.get_weights()
                     )
 
+            # TODO (sven): Use metrics API as soon as we moved to new API stack
+            #  (from currently hybrid stack).
             return train_results

rllib/core/learner/learner.py

@@ -1323,6 +1323,12 @@ def _update_from_batch_or_episodes(
                 },
                 env_steps=sum(len(e) for e in episodes),
             )
+        # Have to convert to MultiAgentBatch.
+        elif isinstance(batch, SampleBatch):
+            assert len(self.module) == 1
+            batch = MultiAgentBatch(
+                {next(iter(self.module.keys())): batch}, env_steps=len(batch)
+            )
 
         # Check the MultiAgentBatch, whether our RLModule contains all ModuleIDs
         # found in this batch. If not, throw an error.

rllib/core/rl_module/marl_module.py

@@ -129,6 +129,10 @@ def keys(self) -> KeysView[ModuleID]:
         """Returns a keys view over the module IDs in this MultiAgentRLModule."""
         return self._rl_modules.keys()
 
+    def __len__(self) -> int:
+        """Returns the number of RLModules within this MultiAgentRLModule."""
+        return len(self._rl_modules)
+
     @override(RLModule)
     def as_multi_agent(self) -> "MultiAgentRLModule":
         """Returns a multi-agent wrapper around this module.

rllib/env/multi_agent_env.py

@@ -530,10 +530,10 @@ def reset(self, *, seed: Optional[int] = None, options: Optional[dict] = None):
         def step(self, action_dict):
             obs, rew, terminated, truncated, info = {}, {}, {}, {}, {}
 
-            # the environment is expecting action for at least one agent
+            # The environment is expecting an action for at least one agent.
             if len(action_dict) == 0:
                 raise ValueError(
-                    "The environment is expecting action for at least one agent."
+                    "The environment is expecting an action for at least one agent."
                 )
 
             for i, action in action_dict.items():

rllib/evaluation/metrics.py

@@ -173,8 +173,12 @@ def summarize_episodes(
         episode_rewards.append(episode.episode_reward)
         for k, v in episode.custom_metrics.items():
             custom_metrics[k].append(v)
-        for (_, policy_id), reward in episode.agent_rewards.items():
-            if policy_id != DEFAULT_POLICY_ID:
+        is_multi_agent = (
+            len(episode.agent_rewards) > 1
+            or DEFAULT_POLICY_ID not in episode.agent_rewards
+        )
+        if is_multi_agent:
+            for (_, policy_id), reward in episode.agent_rewards.items():
                 policy_rewards[policy_id].append(reward)
         for k, v in episode.hist_data.items():
             hist_stats[k] += v

rllib/evaluation/rollout_worker.py

@@ -541,17 +541,19 @@ def wrap(env):
             ):
                 pol._update_model_view_requirements_from_init_state()
 
-        self.multiagent: bool = set(self.policy_map.keys()) != {DEFAULT_POLICY_ID}
-        if self.multiagent and self.env is not None:
-            if not isinstance(
+        if (
+            self.config.is_multi_agent()
+            and self.env is not None
+            and not isinstance(
                 self.env,
                 (BaseEnv, ExternalMultiAgentEnv, MultiAgentEnv, ray.actor.ActorHandle),
-            ):
-                raise ValueError(
-                    f"Have multiple policies {self.policy_map}, but the "
-                    f"env {self.env} is not a subclass of BaseEnv, "
-                    f"MultiAgentEnv, ActorHandle, or ExternalMultiAgentEnv!"
-                )
+            )
+        ):
+            raise ValueError(
+                f"You are running a multi-agent setup, but the env {self.env} is not a "
+                f"subclass of BaseEnv, MultiAgentEnv, ActorHandle, or "
+                f"ExternalMultiAgentEnv!"
+            )
 
         if self.worker_index == 0:
             logger.info("Built filter map: {}".format(self.filters))

rllib/examples/offline_rl/pretrain_bc_single_agent_evaluate_as_multi_agent.py

@@ -0,0 +1,167 @@
+# @HybridAPIStack
+
+"""Example showing how to train a (SA) BC RLModule while evaluating in a MA setup.
+
+Here, SA=single-agent and MA=multi-agent.
+
+Note that the BC Algorithm - by default - runs on the hybrid API stack, using RLModules,
+but not EnvRunners or ConnectorV2s yet.
+
+This example:
+    - demonstrates how you can train a single-agent BC Policy (RLModule) from a JSON
+    file, which contains SampleBatch (expert or non-expert) data.
+    - shows how you can run evaluation in a multi-agent setup (for example vs one
+    or more heuristic policies), while training the BC Policy.
+
+
+How to run this script
+----------------------
+`python [script file name].py --checkpoint-at-end`
+
+For debugging, use the following additional command line options
+`--no-tune --num-env-runners=0`
+which should allow you to set breakpoints anywhere in the RLlib code and
+have the execution stop there for inspection and debugging.
+
+For logging to your WandB account, use:
+`--wandb-key=[your WandB API key] --wandb-project=[some project name]
+--wandb-run-name=[optional: WandB run name (within the defined project)]`
+
+
+Results to expect
+-----------------
+In the console output, you can see that the episode returns of the "main" policy on
+the evaluation track keep increasing as BC manages to more and more clone the behavior
+found in our (expert) JSON file.
+
+After 50-100 iterations, you should see the episode reward reach 450.0.
+Note that the opponent (random) policy does not learn as it's a) not a trainable
+RLModule and b) not being trained via the BCConfig. It's only used for evaluation
+purposes here.
+
++---------------------+------------+-----------------+--------+--------+
+| Trial name          | status     | loc             |   iter |     ts |
+|---------------------+------------+-----------------+--------+--------+
+| BC_None_ee65e_00000 | TERMINATED | 127.0.0.1:35031 |     93 | 203754 |
++---------------------+------------+-----------------+--------+--------+
++----------------------+------------------------+
+|   eps. return (main) |   eps. return (random) |
+|----------------------+------------------------|
+|                452.4 |                   28.3 |
++----------------------+------------------------+
+"""
+import os
+from pathlib import Path
+
+import gymnasium as gym
+
+from ray import tune
+from ray.air.constants import TRAINING_ITERATION
+from ray.rllib.algorithms.bc import BCConfig
+from ray.rllib.examples.envs.classes.multi_agent import MultiAgentCartPole
+from ray.rllib.examples._old_api_stack.policy.random_policy import RandomPolicy
+from ray.rllib.policy.policy import PolicySpec
+from ray.rllib.utils.metrics import (
+    ENV_RUNNER_RESULTS,
+    EVALUATION_RESULTS,
+    NUM_ENV_STEPS_TRAINED,
+)
+from ray.rllib.utils.test_utils import (
+    add_rllib_example_script_args,
+    run_rllib_example_script_experiment,
+)
+from ray.train.constants import TIME_TOTAL_S
+from ray.tune.registry import register_env
+
+parser = add_rllib_example_script_args(
+    default_reward=450.0,
+    default_timesteps=300000,
+)
+parser.set_defaults(num_agents=2)
+
+
+if __name__ == "__main__":
+    args = parser.parse_args()
+
+    register_env("multi_cart", lambda cfg: MultiAgentCartPole(cfg))
+    dummy_env = gym.make("CartPole-v1")
+
+    offline_file = str(
+        Path(os.path.join("../../", "tests/data/cartpole/large.json")).resolve()
+    )
+
+    base_config = (
+        BCConfig()
+        .environment(
+            observation_space=dummy_env.observation_space,
+            action_space=dummy_env.action_space,
+        )
+        .offline_data(
+            input_=offline_file,
+        )
+        .multi_agent(
+            policies={"main"},
+            policy_mapping_fn=lambda *a, **kw: "main",
+        )
+        .evaluation(
+            evaluation_interval=1,
+            evaluation_num_env_runners=0,
+            evaluation_config=BCConfig.overrides(
+                # Evaluate on an actual env -> switch input back to "sampler".
+                input_="sampler",
+                # Do not explore during evaluation, but act greedily.
+                explore=False,
+                # Use a multi-agent setup for evaluation.
+                env="multi_cart",
+                env_config={"num_agents": args.num_agents},
+                policies={
+                    "main": PolicySpec(),
+                    "random": PolicySpec(policy_class=RandomPolicy),
+                },
+                # Only control agent 0 with the main (trained) policy.
+                policy_mapping_fn=(
+                    lambda aid, *a, **kw: "main" if aid == 0 else "random"
+                ),
+                # Note that we do NOT have to specify the `policies_to_train` here,
+                # b/c we are inside the evaluation config (no policy is trained during
+                # evaluation). The fact that the BCConfig above is "only" setup
+                # as single-agent makes it automatically only train the policy found in
+                # the BCConfig's `policies` field (which is "main").
+                # policies_to_train=["main"],
+            ),
+        )
+    )
+
+    policy_eval_returns = (
+        f"{EVALUATION_RESULTS}/{ENV_RUNNER_RESULTS}/policy_reward_mean/"
+    )
+
+    stop = {
+        # Check for the "main" policy's episode return, not the combined one.
+        # The combined one is the sum of the "main" policy + the "random" one.
+        policy_eval_returns + "main": args.stop_reward,
+        NUM_ENV_STEPS_TRAINED: args.stop_timesteps,
+        TRAINING_ITERATION: args.stop_iters,
+    }
+
+    run_rllib_example_script_experiment(
+        base_config,
+        args,
+        stop=stop,
+        # We use a special progress reporter here to show the evaluation results (of the
+        # "main" policy).
+        # In the following dict, the keys are the (possibly nested) keys that can be
+        # found in RLlib's (BC's) result dict, produced at every training iteration, and
+        # the values are the column names you would like to see in your console reports.
+        # Note that for nested result dict keys, you need to use slashes "/" to define
+        # the exact path.
+        progress_reporter=tune.CLIReporter(
+            metric_columns={
+                TRAINING_ITERATION: "iter",
+                TIME_TOTAL_S: "total time (s)",
+                NUM_ENV_STEPS_TRAINED: "ts",
+                policy_eval_returns + "main": "eps. return (main)",
+                policy_eval_returns + "random": "eps. return (random)",
+            }
+        ),
+    )