def _to_w2v_indexes(sentence, w2v_vocab):
    """
    Return which tokens in a sentence cannot be found inside the
    given embedding
    :param sentence: current sentence (tokenized)
    :param w2v_vocab: embedding matrix
    :return: a list of the tokens which were not found
    """
    total_missing = []
    for word in sentence:
        if word in w2v_vocab:
            pass
        elif word.title() in w2v_vocab:
            pass
        elif word.isdigit() or word.find("DIGIT") != -1:
            pass
        else:
            total_missing.append(word)
    return total_missing