models.py

from .. import utils as U
from ..imports import *
from . import preprocessor as tpp

NBSVM = "nbsvm"
FASTTEXT = "fasttext"
LOGREG = "logreg"
BIGRU = "bigru"
STANDARD_GRU = "standard_gru"
BERT = "bert"
DISTILBERT = tpp.DISTILBERT
HUGGINGFACE_MODELS = [DISTILBERT]
LINREG = "linreg"
TEXT_CLASSIFIERS = {
    FASTTEXT: "a fastText-like model [http://arxiv.org/pdf/1607.01759.pdf]",
    LOGREG: "logistic regression using a trainable Embedding layer",
    NBSVM: "NBSVM model [http://www.aclweb.org/anthology/P12-2018]",
    BIGRU: "Bidirectional GRU with pretrained fasttext word vectors [https://fasttext.cc/docs/en/crawl-vectors.html]",
    STANDARD_GRU: "simple 2-layer GRU with randomly initialized embeddings",
    BERT: "Bidirectional Encoder Representations from Transformers (BERT) from keras_bert [https://arxiv.org/abs/1810.04805]",
    DISTILBERT: "distilled, smaller, and faster BERT from Hugging Face transformers [https://arxiv.org/abs/1910.01108]",
}

TEXT_REGRESSION_MODELS = {
    FASTTEXT: "a fastText-like model [http://arxiv.org/pdf/1607.01759.pdf]",
    LINREG: "linear text regression using a trainable Embedding layer",
    BIGRU: "Bidirectional GRU with pretrained English word vectors [https://arxiv.org/abs/1712.09405]",
    STANDARD_GRU: "simple 2-layer GRU with randomly initialized embeddings",
    BERT: "Bidirectional Encoder Representations from Transformers (BERT) - keras_bert implementation [https://arxiv.org/abs/1810.04805]",
    DISTILBERT: "distilled, smaller, and faster BERT from Hugging Face transformers [https://arxiv.org/abs/1910.01108]",
}


def print_text_classifiers():
    for k, v in TEXT_CLASSIFIERS.items():
        print("%s: %s" % (k, v))


def print_text_regression_models():
    for k, v in TEXT_REGRESSION_MODELS.items():
        print("%s: %s" % (k, v))


def calc_pr(y_i, x, y, b):
    idx = np.argwhere((y == y_i) == b)
    ct = x[idx[:, 0]].sum(0) + 1
    tot = ((y == y_i) == b).sum() + 1
    return ct / tot


def calc_r(y_i, x, y):
    return np.log(calc_pr(y_i, x, y, True) / calc_pr(y_i, x, y, False))


def _text_model(
    name,
    train_data,
    preproc=None,
    multilabel=None,
    classification=True,
    metrics=None,
    verbose=1,
):
    """
    ```
    Build and return a text classification or text regression model.

    Args:
        name (string): one of:
                      - 'fasttext' for FastText model
                      - 'nbsvm' for NBSVM model
                      - 'logreg' for logistic regression
                      - 'bigru' for Bidirectional GRU with pretrained word vectors
                      - 'bert' for BERT Text Classification
                      - 'distilbert' for Hugging Face DistilBert model
        train_data (tuple): a tuple of numpy.ndarrays: (x_train, y_train) or ktrain.Dataset instance
                            returned from one of the texts_from_* functions
        preproc: a ktrain.text.TextPreprocessor instance.
                 As of v0.8.0, this is required.
        multilabel (bool):  If True, multilabel model will be returned.
                            If false, binary/multiclass model will be returned.
                            If None, multilabel will be inferred from data.
        classification(bool): If True, will build a text classificaton model.
                              Otherwise, a text regression model will be returned.
        metrics(list): List of metrics to use.  If None: 'accuracy' is used for binar/multiclassification,
                       'binary_accuracy' is used for multilabel classification, and 'mae' is used for regression.
        verbose (boolean): verbosity of output
    Return:
        model (Model): A Keras Model instance
    ```
    """
    # check arguments
    if not isinstance(train_data, tuple) and not U.is_huggingface_from_data(train_data):
        err = """
            Please pass training data in the form of a tuple of numpy.ndarrays
            or data returned from a ktrain texts_from* function.
            """
        raise Exception(err)

    if not isinstance(preproc, tpp.TextPreprocessor):
        msg = "The preproc argument is required."
        msg += " The preproc arg should be an instance of TextPreprocessor, which is "
        msg += " the third return value from texts_from_folder, texts_from_csv, etc."
        # warnings.warn(msg, FutureWarning)
        raise ValueError(msg)
    if name == BIGRU and preproc.ngram_count() != 1:
        raise ValueError("Data should be processed with ngram_range=1 for bigru model.")
    is_bert = U.bert_data_tuple(train_data)
    if (is_bert and name != BERT) or (not is_bert and name == BERT):
        raise ValueError(
            "if '%s' is selected model, then preprocess_mode='%s' should be used and vice versa"
            % (BERT, BERT)
        )
    is_huggingface = U.is_huggingface(data=train_data)
    if (is_huggingface and name not in HUGGINGFACE_MODELS) or (
        not is_huggingface and name in HUGGINGFACE_MODELS
    ):
        raise ValueError(
            "you are using a Hugging Face transformer model but did not preprocess as such (or vice versa)"
        )
    if is_huggingface and preproc.name != name:
        raise ValueError(
            "you preprocessed for %s but want to build a %s model"
            % (preproc.name, name)
        )

    if not classification:  # regression
        if metrics is None or metrics == ["accuracy"]:
            metrics = ["mae"]
        num_classes = 1
        multilabel = False
        loss_func = "mse"
        activation = None
        max_features = preproc.max_features
        features = None
        maxlen = U.shape_from_data(train_data)[1]
        U.vprint("maxlen is %s" % (maxlen), verbose=verbose)
    else:  # classification
        # set number of classes and multilabel flag
        num_classes = U.nclasses_from_data(train_data)

        # determine multilabel
        if multilabel is None:
            multilabel = U.is_multilabel(train_data)
        if multilabel and name in [NBSVM, LOGREG]:
            warnings.warn(
                "switching to fasttext model, as data suggests "
                "multilabel classification from data."
            )
            name = FASTTEXT
        U.vprint("Is Multi-Label? %s" % (multilabel), verbose=verbose)

        # set metrics
        if multilabel and metrics is None:
            metrics = ["binary_accuracy"]
        elif metrics is None:
            metrics = ["accuracy"]

        # set loss and activations
        loss_func = "categorical_crossentropy"
        activation = "softmax"
        if multilabel:
            loss_func = "binary_crossentropy"
            activation = "sigmoid"

        # determine number of classes, maxlen, and max_features
        max_features = preproc.max_features if preproc is not None else None
        features = set()
        if not is_bert and not is_huggingface:
            U.vprint("compiling word ID features...", verbose=verbose)
            x_train = train_data[0]
            y_train = train_data[1]
            if isinstance(y_train[0], int):
                raise ValueError("train labels should not be in sparse format")

            for x in x_train:
                features.update(x)
            # max_features = len(features)
            if max_features is None:
                max_features = max(features) + 1
                U.vprint("max_features is %s" % (max_features), verbose=verbose)
        maxlen = U.shape_from_data(train_data)[1]
        U.vprint("maxlen is %s" % (maxlen), verbose=verbose)

    # return appropriate model
    if name in [LOGREG, LINREG]:
        model = _build_logreg(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
        )

    elif name == FASTTEXT:
        model = _build_fasttext(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
        )
    elif name == STANDARD_GRU:
        model = _build_standard_gru(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
        )
    elif name == NBSVM:
        model = _build_nbsvm(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
            train_data=train_data,
        )

    elif name == BIGRU:
        (tokenizer, tok_dct) = preproc.get_preprocessor()
        model = _build_bigru(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
            tokenizer=tokenizer,
            preproc=preproc,
        )
    elif name == BERT:
        model = _build_bert(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
            preproc=preproc,
        )
    elif name in HUGGINGFACE_MODELS:
        model = _build_transformer(
            num_classes,
            maxlen,
            max_features,
            features,
            loss_func=loss_func,
            activation=activation,
            metrics=metrics,
            verbose=verbose,
            preproc=preproc,
        )

    else:
        raise ValueError("name for textclassifier is invalid")
    U.vprint("done.", verbose=verbose)
    return model


def _build_logreg(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
):
    embedding_matrix = np.ones((max_features, 1))
    embedding_matrix[0] = 0

    # set up the model
    inp = keras.layers.Input(shape=(maxlen,))
    r = keras.layers.Embedding(
        max_features,
        1,
        input_length=maxlen,
        weights=[embedding_matrix],
        trainable=False,
    )(inp)
    x = keras.layers.Embedding(
        max_features,
        num_classes,
        input_length=maxlen,
        embeddings_initializer="glorot_normal",
    )(inp)
    x = keras.layers.dot([x, r], axes=1)
    x = keras.layers.Flatten()(x)
    if activation:
        x = keras.layers.Activation(activation)(x)
    model = keras.Model(inputs=inp, outputs=x)
    model.compile(loss=loss_func, optimizer=U.DEFAULT_OPT, metrics=metrics)
    return model


def _build_bert(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
    preproc=None,
):
    if preproc is None:
        raise ValueError("preproc is missing")
    lang = preproc.lang
    if lang is None:
        raise ValueError("lang is missing")
    config_path = os.path.join(tpp.get_bert_path(lang=lang), "bert_config.json")
    checkpoint_path = os.path.join(tpp.get_bert_path(lang=lang), "bert_model.ckpt")
    check_keras_bert()
    model = keras_bert.load_trained_model_from_checkpoint(
        config_path, checkpoint_path, training=True, trainable=True, seq_len=maxlen
    )
    inputs = model.inputs[:2]
    dense = model.get_layer("NSP-Dense").output
    outputs = keras.layers.Dense(units=num_classes, activation=activation)(dense)
    model = keras.Model(inputs, outputs)
    model.compile(loss=loss_func, optimizer=U.DEFAULT_OPT, metrics=metrics)
    return model


def _build_transformer(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
    preproc=None,
):
    if not isinstance(preproc, tpp.TransformersPreprocessor):
        raise ValueError(
            "preproc must be instance of %s" % (str(tpp.TransformersPreprocessor))
        )

    if loss_func == "mse":
        if preproc.get_classes():
            raise Exception(
                "This is supposed to be regression problem, but preproc.get_classes() is not empty. "
                + "Something went wrong.  Please open a GitHub issue."
            )
            if len(preproc.get_classes()) != num_classes:
                raise Exception(
                    "Number of labels from preproc.get_classes() is not equal to num_classes. "
                    + "Something went wrong. Please open GitHub issue."
                )
    else:
        if not preproc.get_classes():
            raise Exception(
                "This is supposed to be a classification problem, but preproc.get_classes() is empty. "
                + "Something went wrong.  Please open a GitHub issue."
            )
    return (
        preproc.get_regression_model(metrics=metrics)
        if loss_func == "mse"
        else preproc.get_classifier(metrics=metrics)
    )


def _build_nbsvm(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
    train_data=None,
):
    if train_data is None:
        raise ValueError("train_data is required")
    x_train = train_data[0]
    y_train = train_data[1]
    Y = np.array([np.argmax(row) for row in y_train])
    num_columns = max(features) + 1
    num_rows = len(x_train)

    # set up document-term matrix
    X = csr_matrix((num_rows, num_columns), dtype=np.int8)
    # X = lil_matrix((num_rows, num_columns), dtype=np.int8)
    U.vprint(
        "building document-term matrix... this may take a few moments...",
        verbose=verbose,
    )
    r_ids = []
    c_ids = []
    data = []
    for row_id, row in enumerate(x_train):
        trigger = 10000
        trigger_end = min(row_id + trigger, num_rows)
        if row_id % trigger == 0:
            U.vprint("rows: %s-%s" % (row_id + 1, trigger_end), verbose=verbose)
        tmp_c_ids = [column_id for column_id in row if column_id > 0]
        num = len(tmp_c_ids)
        c_ids.extend(tmp_c_ids)
        r_ids.extend([row_id] * num)
        data.extend([1] * num)
    X = csr_matrix((data, (r_ids, c_ids)), shape=(num_rows, num_columns))

    # compute Naive Bayes log-count ratios
    U.vprint("computing log-count ratios...", verbose=verbose)
    nbratios = np.stack([calc_r(i, X, Y).A1 for i in range(num_classes)])
    nbratios = nbratios.T
    embedding_matrix = np.zeros((num_columns, num_classes))
    for i in range(1, num_columns):
        for j in range(num_classes):
            embedding_matrix[i, j] = nbratios[i, j]

    # set up the model
    inp = keras.layers.Input(shape=(maxlen,))
    r = keras.layers.Embedding(
        num_columns,
        num_classes,
        input_length=maxlen,
        weights=[embedding_matrix],
        trainable=False,
    )(inp)
    x = keras.layers.Embedding(
        num_columns, 1, input_length=maxlen, embeddings_initializer="glorot_normal"
    )(inp)
    x = keras.layers.dot([r, x], axes=1)
    x = keras.layers.Flatten()(x)
    x = keras.layers.Activation(activation)(x)
    model = keras.Model(inputs=inp, outputs=x)
    model.compile(loss=loss_func, optimizer=U.DEFAULT_OPT, metrics=metrics)
    return model


def _build_fasttext(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
):
    model = keras.models.Sequential()
    model.add(keras.layers.Embedding(max_features, 64, input_length=maxlen))
    model.add(keras.layers.SpatialDropout1D(0.25))
    model.add(keras.layers.GlobalMaxPool1D())
    model.add(keras.layers.BatchNormalization())
    model.add(keras.layers.Dense(64, activation="relu", kernel_initializer="he_normal"))
    model.add(keras.layers.Dropout(0.5))
    model.add(keras.layers.Dense(num_classes, activation=activation))
    model.compile(loss=loss_func, optimizer=U.DEFAULT_OPT, metrics=metrics)

    return model


def _build_standard_gru(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
):
    model = keras.models.Sequential()
    model.add(keras.layers.Embedding(max_features, 256, input_length=maxlen))
    model.add(keras.layers.GRU(256, dropout=0.9, return_sequences=True))
    model.add(keras.layers.GRU(256, dropout=0.9))
    model.add(keras.layers.Dense(num_classes, activation=activation))
    model.compile(loss=loss_func, optimizer=U.DEFAULT_OPT, metrics=metrics)
    return model


def _build_bigru(
    num_classes,
    maxlen,
    max_features,
    features,
    loss_func="categorical_crossentropy",
    activation="softmax",
    metrics=["accuracy"],
    verbose=1,
    tokenizer=None,
    preproc=None,
):
    if tokenizer is None:
        raise ValueError("bigru requires valid Tokenizer object")
    if preproc is None:
        raise ValueError("bigru requires valid preproc")
    if not hasattr(preproc, "lang") or preproc.lang is None:
        lang = "en"
    else:
        lang = preproc.lang
    wv_url = (
        "https://dl.fbaipublicfiles.com/fasttext/vectors-crawl/cc.%s.300.vec.gz"
        % (lang.split("-")[0])
    )
    if verbose:
        print("word vectors will be loaded from: %s" % (wv_url))

    # setup pre-trained word embeddings
    embed_size = 300
    U.vprint("processing pretrained word vectors...", verbose=verbose)
    embeddings_index = tpp.load_wv(wv_path_or_url=wv_url, verbose=verbose)
    word_index = tokenizer.word_index
    # nb_words = min(max_features, len(word_index))
    nb_words = max_features
    embedding_matrix = np.zeros((nb_words, embed_size))
    for word, i in word_index.items():
        if i >= max_features:
            continue
        embedding_vector = embeddings_index.get(word)
        if embedding_vector is not None:
            embedding_matrix[i] = embedding_vector

    # define model
    inp = keras.layers.Input(shape=(maxlen,))
    x = keras.layers.Embedding(max_features, embed_size, weights=[embedding_matrix])(
        inp
    )
    x = keras.layers.SpatialDropout1D(0.2)(x)
    x = keras.layers.Bidirectional(keras.layers.GRU(80, return_sequences=True))(x)
    avg_pool = keras.layers.GlobalAveragePooling1D()(x)
    max_pool = keras.layers.GlobalMaxPool1D()(x)
    conc = keras.layers.concatenate([avg_pool, max_pool])
    outp = keras.layers.Dense(num_classes, activation=activation)(conc)
    model = keras.Model(inputs=inp, outputs=outp)
    model.compile(loss=loss_func, optimizer=U.DEFAULT_OPT, metrics=metrics)
    return model


def text_classifier(
    name, train_data, preproc=None, multilabel=None, metrics=None, verbose=1
):
    """
    ```
    Build and return a text classification model.

    Args:
        name (string): one of:
                      - 'fasttext' for FastText model
                      - 'nbsvm' for NBSVM model
                      - 'logreg' for logistic regression using embedding layers
                      - 'bigru' for Bidirectional GRU with pretrained word vectors
                      - 'bert' for BERT Text Classification
                      - 'distilbert' for Hugging Face DistilBert model

        train_data (tuple): a tuple of numpy.ndarrays: (x_train, y_train) or ktrain.Dataset instance
                            returned from one of the texts_from_* functions
        preproc: a ktrain.text.TextPreprocessor instance.
                 As of v0.8.0, this is required.
        multilabel (bool):  If True, multilabel model will be returned.
                            If false, binary/multiclass model will be returned.
                            If None, multilabel will be inferred from data.
        metrics(list): List of metrics to use.  If None: 'accuracy' is used for binar/multiclassification,
                       'binary_accuracy' is used for multilabel classification, and 'mae' is used for regression.
        verbose (boolean): verbosity of output
    Return:
        model (Model): A Keras Model instance
    ```
    """
    if name not in TEXT_CLASSIFIERS:
        raise ValueError("invalid name for text classification: %s" % (name))
    if preproc is not None and not preproc.get_classes():
        raise ValueError(
            "preproc.get_classes() is empty, but required for text classification"
        )
    return _text_model(
        name,
        train_data,
        preproc=preproc,
        multilabel=multilabel,
        classification=True,
        metrics=metrics,
        verbose=verbose,
    )


def text_regression_model(name, train_data, preproc=None, metrics=["mae"], verbose=1):
    """
    ```
    Build and return a text regression model.

    Args:
        name (string): one of:
                      - 'fasttext' for FastText model
                      - 'nbsvm' for NBSVM model
                      - 'linreg' for linear regression using embedding layers
                      - 'bigru' for Bidirectional GRU with pretrained word vectors
                      - 'bert' for BERT Text Classification
                      - 'distilbert' for Hugging Face DistilBert model

        train_data (tuple): a tuple of numpy.ndarrays: (x_train, y_train)
        preproc: a ktrain.text.TextPreprocessor instance.
                 As of v0.8.0, this is required.
        metrics(list): metrics to use
        verbose (boolean): verbosity of output
    Return:
        model (Model): A Keras Model instance
    ```
    """
    if name not in TEXT_REGRESSION_MODELS:
        raise ValueError("invalid name for text classification: %s" % (name))
    if preproc is not None and preproc.get_classes():
        raise ValueError(
            "preproc.get_classes() is supposed to be empty for text regression tasks"
        )
    return _text_model(
        name,
        train_data,
        preproc=preproc,
        multilabel=False,
        classification=False,
        metrics=metrics,
        verbose=verbose,
    )