train_multiclass_model.py

# IMPORTS

import pandas as pd
import nltk
nltk.download("punkt")
from nltk import tokenize
import time
from sklearn.model_selection import train_test_split
from transformers import BertConfig, BertTokenizer, TFBertModel
from tensorflow.keras.preprocessing.sequence import pad_sequences
from tensorflow import convert_to_tensor
from tensorflow.keras.layers import Input, Dense
from tensorflow.keras.initializers import TruncatedNormal
from tensorflow.keras.models import Model
from tensorflow.keras.optimizers import Adam
from tensorflow.keras.metrics import CategoricalAccuracy, Precision, Recall


# SET PARAMETERS

DATA_PATH="..."

SAVE_MODEL_TO=".../"


# READ DATA

tab=pd.read_hdf(DATA_PATH)


# PREPARE DATA FOR BERT

def data_to_values(dataframe):
    """Converts data to values.
    """
    abstracts=dataframe.Abstract.values
    labels=dataframe.Label.values
    return abstracts, labels
    

def tokenize_abstracts(abstracts):
    """For given texts, adds '[CLS]' and '[SEP]' tokens
    at the beginning and the end of each sentence, respectively.
    """
    t_abstracts=[]
    for abstract in abstracts:
        t_abstract="[CLS] "
        for sentence in tokenize.sent_tokenize(abstract):
            t_abstract=t_abstract + sentence + " [SEP] "
        t_abstracts.append(t_abstract)
    return t_abstracts


tokenizer=BertTokenizer.from_pretrained('bert-base-multilingual-uncased')


def b_tokenize_abstracts(t_abstracts, max_len=512):
    """Tokenizes sentences with the help
    of a 'bert-base-multilingual-uncased' tokenizer.
    """
    b_t_abstracts=[tokenizer.tokenize(_)[:max_len] for _ in t_abstracts]
    return b_t_abstracts


def convert_to_ids(b_t_abstracts):
    """Converts tokens to its specific
    IDs in a bert vocabulary.
    """
    input_ids=[tokenizer.convert_tokens_to_ids(_) for _ in b_t_abstracts]
    return input_ids


def abstracts_to_ids(abstracts):
    """Tokenizes abstracts and converts
    tokens to their specific IDs
    in a bert vocabulary.
    """
    tokenized_abstracts=tokenize_abstracts(abstracts)
    b_tokenized_abstracts=b_tokenize_abstracts(tokenized_abstracts)
    ids=convert_to_ids(b_tokenized_abstracts)
    return ids


def pad_ids(input_ids, max_len=512):
    """Padds sequences of a given IDs.
    """
    p_input_ids=pad_sequences(input_ids,
                                maxlen=max_len,
                                dtype="long",
                                truncating="post",
                                padding="post")
    return p_input_ids


def create_attention_masks(inputs):
    """Creates attention masks
    for a given seuquences.
    """
    masks=[]
    for sequence in inputs:
        sequence_mask=[float(_>0) for _ in sequence]
        masks.append(sequence_mask)
    return masks


# CREATE MODEL

def create_model():
    config=BertConfig.from_pretrained(
                                    "bert-base-multilingual-uncased",
                                    num_labels=16,
                                    hidden_dropout_prob=0.2,
                                    attention_probs_dropout_prob=0.2)
    bert=TFBertModel.from_pretrained(
                                    "bert-base-multilingual-uncased",
                                    config=config)
    bert_layer=bert.layers[0]
    input_ids_layer=Input(
                        shape=(512),
                        name="input_ids",
                        dtype="int32")
    input_attention_masks_layer=Input(
                                    shape=(512),
                                    name="attention_masks",
                                    dtype="int32")
    bert_model=bert_layer(
                        input_ids_layer,
                        input_attention_masks_layer)
    target_layer=Dense(
                    units=16,
                    kernel_initializer=TruncatedNormal(stddev=config.initializer_range),
                    name="target_layer",
                    activation="softmax")(bert_model[1])
    model=Model(
                inputs=[input_ids_layer, input_attention_masks_layer],
                outputs=target_layer,
                name="mbert_multiclass_16")
    optimizer=Adam(
                learning_rate=5e-05,
                epsilon=1e-08,
                decay=0.01,
                clipnorm=1.0)
    model.compile(
                optimizer=optimizer,
                loss="categorical_crossentropy", 
                metrics=[CategoricalAccuracy(), Precision(), Recall()])
    return model


abstracts, labels=data_to_values(tab)
ids=abstracts_to_ids(abstracts)
print("Abstracts tokenized, tokens converted to ids.")

padded_ids=pad_ids(ids)
print("Sequences padded.")

train_inputs, temp_inputs, train_labels, temp_labels=train_test_split(padded_ids, labels, random_state=1993, test_size=0.3)
validation_inputs, test_inputs, validation_labels, test_labels=train_test_split(temp_inputs, temp_labels, random_state=1993, test_size=0.5)
print("Data splited into train, validation, test sets.")

train_masks, validation_masks, test_masks=[create_attention_masks(_) for _ in [train_inputs, validation_inputs, test_inputs]]
print("Attention masks created.")
train_inputs, validation_inputs, test_inputs=[convert_to_tensor(_) for _ in [train_inputs, validation_inputs, test_inputs]]
print("Inputs converted to tensors.")
train_labels, validation_labels, test_labels=[convert_to_tensor(_) for _ in [train_labels, validation_labels, test_labels]]
print("Labels converted to tensors.")
train_masks, validation_masks, test_masks=[convert_to_tensor(_) for _ in [train_masks, validation_masks, test_masks]]
print("Masks converted to tensors.")


model=create_model()
print("Model initialized.")


history=model.fit([train_inputs, train_masks], train_labels,
                        batch_size=8,
                        epochs=2,
                        validation_data=([validation_inputs, validation_masks], validation_labels))


model.save(SAVE_MODEL_TO+"mbert_multiclass_16.h5")
print("Model saved.")

test_score=model.evaluate([test_inputs, test_masks], test_labels,
                            batch_size=8)

print("Model tested.")


stats=pd.DataFrame(test_score, columns=["loss", "accuracy", "precision", "recall"])
stats.to_excel(SAVE_MODEL_TO+"mbert_multiclass_16_stats.xlsx", index=False)

print("Stats saved.")