Write a loop-up file that contains the direct (record-wise) lookup
    information.

    Parameters
    ----------
    feature_folder :
        Path to the feature files.
    dataset_name :
        'traindata', 'validdata' or 'testdata'.
    translation : list of triples
        (raw data id, formula in latex, formula id)

def _create_translation_file(feature_folder,
                             dataset_name,
                             translation,
                             formula_id2index):
    """
    Write a loop-up file that contains the direct (record-wise) lookup
    information.

    Parameters
    ----------
    feature_folder :
        Path to the feature files.
    dataset_name :
        'traindata', 'validdata' or 'testdata'.
    translation : list of triples
        (raw data id, formula in latex, formula id)
    """
    translationfilename = "%s/translation-%s.csv" % (feature_folder,
                                                     dataset_name)
    with open(translationfilename, "w") as f:
        f.write("index,raw_data_id,latex,formula_id\n")
        for el in translation:
            f.write("%i,%i,%s,%i\n" % (formula_id2index[el[2]],
                                       el[0], el[1], el[2]))