Collecting a subset of a dictionary space with StepDataCallback#

In this tutorial you’ll learn how to have minari.DataCollector only collect a subset of the observation space in PointMaze. Specifically, we’ll be collecting observations using random actions on PointMaze_UMaze-v3 from Gymnasium-Robotics and omitting achieved_goal from the observation space of PointMaze. This would be useful if you don’t plan on training goal oriented learning agents on the Minari dataset generated and need to minimize the space taken up by the final dataset.

Please note that while only a subset of the observation space of PointMaze is touched on in this tutorial, the outlined procedure can be extended to both action/observation spaces of any other environment.

Let’s get started by importing the required modules:

import gymnasium as gym
import numpy as np
from gymnasium import spaces

import minari
from minari import DataCollector
from minari.data_collector.callbacks import StepDataCallback

We’ll first need to initialize our PointMaze_UMaze environment and find the shape of the observation space

env = gym.make("PointMaze_UMaze-v3")

print(f"Observation space: {env.observation_space}")

Which should output:

Observation space: Dict('achieved_goal': Box(-inf, inf, (2,), float64), 'desired_goal': Box(-inf, inf, (2,), float64), 'observation': Box(-inf, inf, (4,), float64))

We now need to create a version of the observation space with achieved_goal omitted using Gymnasium spaces. This will be compared with step_data in each step to validate that it fits with the expected observation space. When saving the final HDF5 dataset file generated by Mirana to disk, this will be added as metadata.

We’ll also need to define a minari.StepDataCallback in order to modify step_data to delete achieved_goal.

observation_space_subset = spaces.Dict(
        # "achieved_goal": spaces.Box(low=float('-inf'), high=float('inf'), shape=(2,), dtype=np.float64),
        "desired_goal": spaces.Box(
            low=float("-inf"), high=float("inf"), shape=(2,), dtype=np.float64
        "observation": spaces.Box(
            low=float("-inf"), high=float("inf"), shape=(4,), dtype=np.float64

class CustomSubsetStepDataCallback(StepDataCallback):
    def __call__(self, env, **kwargs):
        step_data = super().__call__(env, **kwargs)
        del step_data["observations"]["achieved_goal"]
        return step_data

Finally we’ll record 10 episodes with our observation space subset and callback passed to minari.DataCollector.

dataset_id = "point-maze-subseted-v3"

# delete the test dataset if it already exists
local_datasets = minari.list_local_datasets()
if dataset_id in local_datasets:

env = DataCollector(
    # action_space=action_space_subset,
num_episodes = 10


for episode in range(num_episodes):
    terminated = False
    truncated = False
    while not terminated and not truncated:
        action = env.action_space.sample()  # Choose random actions
        _, _, terminated, truncated, _ = env.step(action)

# Create Minari dataset and store locally
dataset = env.create_dataset(


The output from the final line above, should be

dict_keys(['desired_goal', 'observation'])

Showing that we have successfully omitted achieved_goal from the observations.