List of dictionary features get standardized

[sohamparikh94]

Describe the bug

Hi, i’m trying to create a HF dataset from a list using Dataset.from_list.

Each sample in the list is a dict with the same keys (which will be my features). The values for each feature are a list of dictionaries, and each such dictionary has a different set of keys. However, the datasets library standardizes all dictionaries under a feature and adds all possible keys (with None value) from all the dictionaries under that feature.

How can I keep the same set of keys as in the original list for each dictionary under a feature?

Steps to reproduce the bug

from datasets import Dataset

# Define a function to generate a sample with "tools" feature
def generate_sample():
    # Generate random sample data
    sample_data = {
        "text": "Sample text",
        "feature_1": []
    }

    # Add feature_1 with random keys for this sample
    feature_1 = [{"key1": "value1"}, {"key2": "value2"}]  # Example feature_1 with random keys
    sample_data["feature_1"].extend(feature_1)

    return sample_data

# Generate multiple samples
num_samples = 10
samples = [generate_sample() for _ in range(num_samples)]

# Create a Hugging Face Dataset
dataset = Dataset.from_list(samples)
dataset[0]

{'text': 'Sample text', 'feature_1': [{'key1': 'value1', 'key2': None}, {'key1': None, 'key2': 'value2'}]}

Expected behavior

{'text': 'Sample text', 'feature_1': [{'key1': 'value1'}, {'key2': 'value2'}]}

Environment info

• datasets version: 2.19.1
• Platform: Linux-5.15.0-1040-nvidia-x86_64-with-glibc2.35
• Python version: 3.10.13
• huggingface_hub version: 0.23.0
• PyArrow version: 15.0.0
• Pandas version: 2.2.0
• fsspec version: 2023.10.0