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@@ -141,52 +141,6 @@ We have upload most of the OpenX datasets in [huggingface](https://huggingface.c
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You can visualize the dataset in this [space](https://huggingface.co/spaces/IPEC-COMMUNITY/openx_dataset_lerobot_v2.0).
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## The `LeRobotDataset` format
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A dataset in `LeRobotDataset` format is very simple to use. It can be loaded from a repository on the Hugging Face hub or a local folder simply with e.g. `dataset = LeRobotDataset("lerobot/aloha_static_coffee")` and can be indexed into like any Hugging Face and PyTorch dataset. For instance `dataset[0]` will retrieve a single temporal frame from the dataset containing observation(s) and an action as PyTorch tensors ready to be fed to a model.
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A specificity of `LeRobotDataset` is that, rather than retrieving a single frame by its index, we can retrieve several frames based on their temporal relationship with the indexed frame, by setting `delta_timestamps` to a list of relative times with respect to the indexed frame. For example, with `delta_timestamps = {"observation.image": [-1, -0.5, -0.2, 0]}` one can retrieve, for a given index, 4 frames: 3 "previous" frames 1 second, 0.5 seconds, and 0.2 seconds before the indexed frame, and the indexed frame itself (corresponding to the 0 entry). See example [1_load_lerobot_dataset.py](examples/1_load_lerobot_dataset.py) for more details on `delta_timestamps`.
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Under the hood, the `LeRobotDataset` format makes use of several ways to serialize data which can be useful to understand if you plan to work more closely with this format. We tried to make a flexible yet simple dataset format that would cover most type of features and specificities present in reinforcement learning and robotics, in simulation and in real-world, with a focus on cameras and robot states but easily extended to other types of sensory inputs as long as they can be represented by a tensor.
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Here are the important details and internal structure organization of a typical `LeRobotDataset` instantiated with `dataset = LeRobotDataset("lerobot/aloha_static_coffee")`. The exact features will change from dataset to dataset but not the main aspects:
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```
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dataset attributes:
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├ hf_dataset: a Hugging Face dataset (backed by Arrow/parquet). Typical features example:
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│ ├ observation.images.cam_high (VideoFrame):
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│ │ VideoFrame = {'path': path to a mp4 video, 'timestamp' (float32): timestamp in the video}
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│ ├ observation.state (list of float32): position of an arm joints (for instance)
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│ ... (more observations)
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│ ├ action (list of float32): goal position of an arm joints (for instance)
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│ ├ episode_index (int64): index of the episode for this sample
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│ ├ frame_index (int64): index of the frame for this sample in the episode ; starts at 0 for each episode
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│ ├ timestamp (float32): timestamp in the episode
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│ ├ next.done (bool): indicates the end of en episode ; True for the last frame in each episode
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│ └ index (int64): general index in the whole dataset
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├ episode_data_index: contains 2 tensors with the start and end indices of each episode
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│ ├ from (1D int64 tensor): first frame index for each episode — shape (num episodes,) starts with 0
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│ └ to: (1D int64 tensor): last frame index for each episode — shape (num episodes,)
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├ stats: a dictionary of statistics (max, mean, min, std) for each feature in the dataset, for instance
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│ ├ observation.images.cam_high: {'max': tensor with same number of dimensions (e.g. `(c, 1, 1)` for images, `(c,)` for states), etc.}
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│ ...
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├ info: a dictionary of metadata on the dataset
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│ ├ codebase_version (str): this is to keep track of the codebase version the dataset was created with
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│ ├ fps (float): frame per second the dataset is recorded/synchronized to
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│ ├ video (bool): indicates if frames are encoded in mp4 video files to save space or stored as png files
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│ └ encoding (dict): if video, this documents the main options that were used with ffmpeg to encode the videos
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├ videos_dir (Path): where the mp4 videos or png images are stored/accessed
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└ camera_keys (list of string): the keys to access camera features in the item returned by the dataset (e.g. `["observation.images.cam_high", ...]`)
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```
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A `LeRobotDataset` is serialised using several widespread file formats for each of its parts, namely:
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- hf_dataset stored using Hugging Face datasets library serialization to parquet
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- videos are stored in mp4 format to save space
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- metadata are stored in plain json/jsonl files
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Dataset can be uploaded/downloaded from the HuggingFace hub seamlessly. To work on a local dataset, you can use the `local_files_only` argument and specify its location with the `root` argument if it's not in the default `~/.cache/huggingface/lerobot` location.
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## Acknowledgment
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Special thanks to the [Lerobot teams](https://github.com/huggingface/lerobot) for making this great framework.
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