def flat_config(config):
    """Flat config loaded from a yaml file to a flat dict.
    
    Args:
        config (dict): Configuration loaded from a yaml file.

    Returns:
        dict: Configuration dictionary.
    """
    f_config = {}
    category = config.keys()
    for cate in category:
        for key, val in config[cate].items():
            f_config[key] = val
    return f_config