Issue for converting bio sequence

[ihungalexhsu]

Hi @jgmf-amazon, thanks for your reply. However, the current evaluation code contains some issue:

def convert_to_bio(seq_tags, outside='Other', labels_merge=None):
    """
    Converts a sequence of tags into BIO format. EX:

        ['city', 'city', 'Other', 'country', -100, 'Other']
        to
        ['B-city', 'I-city', 'O', 'B-country', 'I-country', 'O']
        where outside = 'Other' and labels_merge = [-100]

    :param seq_tags: the sequence of tags that should be converted
    :type seq_tags: list
    :param outside: The label(s) to put outside (ignore). Default: 'Other'
    :type outside: str or list
    :param labels_merge: The labels to merge leftward (i.e. for tokenized inputs)
    :type labels_merge: str or list
    :return: a BIO-tagged sequence
    :rtype: list
    """

    seq_tags = [str(x) for x in seq_tags]

    outside = [outside] if type(outside) != list else outside
    outside = [str(x) for x in outside]

    if labels_merge:
        labels_merge = [labels_merge] if type(labels_merge) != list else labels_merge
        labels_merge = [str(x) for x in labels_merge]
    else:
        labels_merge = []

    bio_tagged = []
    prev_tag = None
    for tag in seq_tags:
        if tag in outside:
            bio_tagged.append('O')
            prev_tag = tag
            continue
        if tag != prev_tag and tag not in labels_merge:
            bio_tagged.append('B-' + tag)
            prev_tag = tag
            continue
        if tag == prev_tag or tag in labels_merge:
            if prev_tag in outside:
                bio_tagged.append('O')
            else:
                bio_tagged.append('I-' + prev_tag)

    return bio_tagged

The current code will meet a bug when:
prev_tag is None and tag is -100.
This will not happen if model is properly trained, but when train the model at the beginning stage, the model might output this silly combination.

Maybe a potential solution is not initialized prev_tag with None, but using 'O'?

Originally posted by @ihungalexhsu in #13 (comment)

[jgmf-amazon]

Hi @ihungalexhsu , good catch. How does this look?

6a12822

[ihungalexhsu]

Yeah, I think this test case looks good!

[cperiz]

Thanks @ihungalexhsu. Merged PR.