include ../../_includes/_mixins

p
    |  All #[+a("/docs/usage/models") spaCy models] support online learning, so
    |  you can update a pre-trained model with new examples. You can even add
    |  new classes to an existing model, to recognise a new entity type,
    |  part-of-speech, or syntactic relation. Updating an existing model is
    |  particularly useful as a "quick and dirty solution", if you have only a
    |  few corrections or annotations.

+h(2, "improving-accuracy") Improving accuracy on existing entity types

p
    |  To update the model, you first need to create an instance of
    |  #[+api("goldparse") #[code GoldParse]], with the entity labels
    |  you want to learn. You'll usually need to provide many examples to
    |  meaningfully improve the system — a few hundred is a good start, although
    |  more is better.

+image
    include ../../assets/img/docs/training-loop.svg
    .u-text-right
        +button("/assets/img/docs/training-loop.svg", false, "secondary").u-text-tag View large graphic

p
    |  You should avoid iterating over the same few examples multiple times, or
    |  the model is likely to "forget" how to annotate other examples. If you
    |  iterate over the same few examples, you're effectively changing the loss
    |  function. The optimizer will find a way to minimize the loss on your
    |  examples, without regard for the consequences on the examples it's no
    |  longer paying attention to.

p
    |  One way to avoid this "catastrophic forgetting" problem is to "remind"
    |  the model of other examples by augmenting your annotations with sentences
    |  annotated with entities automatically recognised by the original model.
    |  Ultimately, this is an empirical process: you'll need to
    |  #[strong experiment on your own data] to find a solution that works best
    |  for you.

+h(2, "example") Example

+under-construction

+code.
    import random
    from spacy.lang.en import English
    from spacy.gold import GoldParse, biluo_tags_from_offsets

    def main(model_dir=None):
        train_data = [
            ('Who is Shaka Khan?',
                [(len('Who is '), len('Who is Shaka Khan'), 'PERSON')]),
            ('I like London and Berlin.',
                [(len('I like '), len('I like London'), 'LOC'),
                (len('I like London and '), len('I like London and Berlin'), 'LOC')])
        ]
        nlp = English(pipeline=['tensorizer', 'ner'])
        get_data = lambda: reformat_train_data(nlp.tokenizer, train_data)
        optimizer = nlp.begin_training(get_data)
        for itn in range(100):
            random.shuffle(train_data)
            losses = {}
            for raw_text, entity_offsets in train_data:
                doc = nlp.make_doc(raw_text)
                gold = GoldParse(doc, entities=entity_offsets)
                nlp.update([doc], [gold], drop=0.5, sgd=optimizer, losses=losses)
        nlp.to_disk(model_dir)

+code.
    def reformat_train_data(tokenizer, examples):
        """Reformat data to match JSON format"""
        output = []
        for i, (text, entity_offsets) in enumerate(examples):
            doc = tokenizer(text)
            ner_tags = biluo_tags_from_offsets(tokenizer(text), entity_offsets)
            words = [w.text for w in doc]
            tags = ['-'] * len(doc)
            heads = [0] * len(doc)
            deps = [''] * len(doc)
            sentence = (range(len(doc)), words, tags, heads, deps, ner_tags)
            output.append((text, [(sentence, [])]))
        return output

p.u-text-right
    +button(gh("spaCy", "examples/training/train_ner.py"), false, "secondary").u-text-tag View full example

+h(2, "saving-loading") Saving and loading

p
    |  After training our model, you'll usually want to save its state, and load
    |  it back later. You can do this with the
    |  #[+api("language#to_disk") #[code Language.to_disk()]] method:

+code.
    nlp.to_disk('/home/me/data/en_technology')

p
    |  To make the model more convenient to deploy, we recommend wrapping it as
    |  a Python package, so that you can install it via pip and load it as a
    |  module. spaCy comes with a handy #[+api("cli#package") #[code package]]
    |  CLI command to create all required files and directories.

+code(false, "bash").
    python -m spacy package /home/me/data/en_technology /home/me/my_models

p
    |  To build the package and create a #[code .tar.gz] archive, run
    |  #[code python setup.py sdist] from within its directory.

+infobox("Saving and loading models")
    |  For more information and a detailed guide on how to package your model,
    |  see the documentation on
    |  #[+a("/docs/usage/saving-loading#models") saving and loading models].
