def get_list_of_subsets(subset_task):
    """
    Get the subsets to process for this analysis

    Parameters:
    -----------
    subset_task:    string
        string which specifies which subsets to use

    Results:
    --------
    list of subset tasks
    """
    # prefix for data and images
    if subset_task == 'all':
        subset_list = ['train', 'valid', 'test']
    elif subset_task == 'train':
        subset_list = ['train']
    elif subset_task == 'valid':
        subset_list = ['valid']
    elif subset_task == 'test':
        subset_list = ['test']
    else:
        raise ValueError('task value does not match to the expected value', subset_task)

    return subset_list