multiworld

Multitask Environments for RL

Basic Usage

This library contains a variety of gym GoalEnvs.

As a running example, let's say we have a CarEnv. Like normal gym envs, we can do

env = CarEnv()
obs = env.reset()
next_obs, reward, done, info = env.step(action)

Unlike Envs, the observation space of GoalEnvs is a dictionary.

print(obs)

# Output:
# {
#     'observation': ...,
#     'desired_goal': ...,
#     'achieved_goal': ...,
# }

This can make it rather difficult to use these envs with existing RL code, which usually expects a flat vector. Hence, we include a wrapper that converts this dictionary-observation env into a normal "flat" environment:

base_env = CarEnv()
env = FlatGoalEnv(base_env, obs_key='observation')
obs = env.reset()  # returns just the 'observation'
action = policy_that_takes_in_vector(obs)

The observation space of FlatGoalEnv will be the corresponding env of the vector (e.g. gym.space.Box). However, note that the goal is not part of the observation! Not giving the goal to the policy might make the task impossible.

We provide two possible solutions to this:

1. Use the get_goal function

base_env = CarEnv()
env = FlatGoalEnv(base_env, obs_key='observation')
obs = env.reset()  # returns just the 'observation'
goal = env.get_goal()
action = policy_that_takes_in_two_vectors(obs, goal)

2. Pass in a list including 'desired_goal' to FlatGoalEnv and set append_goal_to_obs to True.

base_env = CarEnv()
env = FlatGoalEnv(
    base_env,
    obs_key=['observation', 'desired_goal'],
    append_goal_to_obs=True,  # default value is False
)
obs = env.reset()  # returns 'observation' concatenated to `desired_goal`
action = policy_that_takes_in_vector(obs)

Extending Obs/Goals - Debugging and Multi-Modality

One nice thing about using Dict spaces + FlatGoalEnv is that it makes it really easy to extend and debug.

For example, this repo includes an ImageMujocoEnv wrapper which converts the observation space of a Mujoco GoalEnv into images. Rather than completely overwriting observation, we simply append the images to the dictionary:

base_env = CarEnv()
env = ImageEnv(base_env)
obs = env.reset()

print(obs)

# Output:
# {
#     'observation': ...,
#     'desired_goal': ...,
#     'achieved_goal': ...,
#     'image_observation': ...,
#     'image_desired_goal': ...,
#     'image_achieved_goal': ...,
#     'state_observation': ...,   # CarEnv sets these values by default
#     'state_desired_goal': ...,
#     'state_achieved_goal': ...,
# }

This makes it really easy to debug your environment, by e.g. using state-based observation but image-based goals:

base_env = CarEnv()
wrapped_env = ImageEnv(base_env)
env = FlatGoalEnv(
    base_env,
    obs_key='state_observation',
    goal_key='image_desired_goal',
)

It also makes multi-model environments really easy to write!

base_env = CarEnv()
wrapped_env = ImageEnv(base_env)
wrapped_env = LidarEnv(wrapped_env)
wrapped_env = LanguageEnv(wrapped_env)
env = FlatGoalEnv(
    base_env,
    obs_key=['image_observation', 'lidar_observation'],
    goal_key=['language_desired_goal', 'image_desired_goal'],
)
obs = env.reset()  # image + lidar observation
goal = env.get_goal()  # language + image goal

Note that you don't have to use FlatGoalEnv: you can always just use the environments manually choose the keys that you care about from the observation.

WARNING: compute_reward incompatibility

The compute_reward interface is slightly different from gym's. Rather than compute_reward(desired_goal, achieved_goal, info) our interface is compute_reward(action, observation), where the observation is a dictionary.

Extra features

fixed_goal

The environments also all taken in fixed_goal as a parameter, which disables resampling the goal each time reset is called. This can be useful for debugging: first make sure the env can solve the single-goal case before trying the multi-goal case.

get_diagnostics

The function get_diagonstics(rollouts) returns an OrderedDict of potentially useful numbers to plot/log. rollouts is a list. Each element of the list should be a dictionary describing a rollout. A dictionary should have the following keys with the corresponding values:

{
    'observations': np array,
    'actions': np array,
    'next_observations': np array,
    'rewards': np array,
    'terminals': np array,
    'env_infos': list of dictionaries returned by step(),
}