Menu iconMenu iconIntroduction to Natural Language Processing with Transformers
Introduction to Natural Language Processing with Transformers

Chapter 7: Prominent Transformer Models and Their Applications

7.3 Understanding the BERT Output

When we pass our tokenized inputs through the model, BERT gives us a sequence of hidden-states which is the activations of the last layer of the model. This process is fundamental to the functioning of BERT, as it allows the model to create a representation of the text that is more nuanced and contextualized.

This output is a sequence of contextual word embeddings i.e., each word gets an embedding which depends on the other words in the sentence. This means that the model is able to capture the complex relationships between words in a sentence, and provide a more accurate representation of the meaning of the text. In addition, we get a pooled output which is a summary of the content of the sentence.

This summary is an aggregation of the contextual word embeddings, and provides a higher-level representation of the text that can be used for downstream tasks such as sentiment analysis or information retrieval. Overall, the process of passing tokenized inputs through a BERT model is a powerful tool for natural language processing, allowing for more nuanced and accurate representations of text.

For instance:

from transformers import BertModel

model = BertModel.from_pretrained('bert-base-uncased')
outputs = model(**inputs)
last_hidden_state = outputs.last_hidden_state
pooled_output = outputs.pooler_output
  • last_hidden_state: This is a sequence of hidden states of the last layer of the model. It is a tensor of shape (batch_size, sequence_length, hidden_size). We can use these to get a sequence of contextual word embeddings.
  • pooled_output: This is a pooled representation of the last_hidden_state. It is a tensor of shape (batch_size, hidden_size). This can be used as an embedding for the entire sentence.

We are now equipped with a solid understanding of how to preprocess text data for transformer models, and how to work with their output. This is all the knowledge we need to dive into our first project: Sentiment Analysis with BERT.

Project 1: Sentiment Analysis with BERT

Sentiment Analysis is a classic NLP problem where the goal is to classify text according to the sentiment expressed in it. For instance, the sentence "I love this movie!" expresses a positive sentiment, while "I hate this movie!" expresses a negative sentiment. In this project, we will build a sentiment analysis model using BERT.

Let's start by defining the problem more formally:

Problem Definition

Problem: Classify sentences into their corresponding sentiment. The sentiments could be positive, negative, or neutral.

Data: The data is composed of sentences and their corresponding sentiment labels. For the sake of this example, we'll assume a binary classification task (positive and negative sentiment), but this could easily be extended to a multi-class problem (including neutral sentiment).

Example:

Sentence: "I love this movie!"

Label: Positive

Sentence: "I hate this movie!"

Label: Negative

Data Preparation

The first step in any machine learning project is preparing the data. We will need a labeled dataset composed of sentences and their corresponding sentiment labels. There are many such datasets available publicly, one of which is the IMDB movie reviews dataset.

We can load and preprocess this data using the Hugging Face datasets library:

from datasets import load_dataset

# Load the dataset
dataset = load_dataset("imdb")

# Print a few examples
print(dataset['train'][0])

This will load the IMDB dataset and print out the first training example. Each example consists of a text (the review) and a label (0 or 1, corresponding to negative or positive sentiment).

Model Training

Once we have prepared the data, we can move on to training our model. First, we tokenize our data:

from transformers import BertTokenizerFast

# Load the BERT tokenizer
tokenizer = BertTokenizerFast.from_pretrained('bert-base-uncased')

# Tokenize the data
train_encodings = tokenizer(dataset['train']['text'], truncation=True, padding=True)

Next, we prepare our data for the PyTorch framework:

import torch

# Prepare PyTorch Dataset
class IMDBDataset(torch.utils.data.Dataset):
    def __init__(self, encodings, labels):
        self.encodings = encodings
        self.labels = labels

    def __getitem__(self, idx):
        item = {key: torch.tensor(val[idx]) for key, val in self.encodings.items()}
        item['labels'] = torch.tensor(self.labels[idx])
        return item

    def __len__(self):
        return len(self.labels)

# Create the Dataset
train_dataset = IMDBDataset(train_encodings, dataset['train']['label'])

Finally, we train our model:

from transformers import BertForSequenceClassification, Trainer, TrainingArguments

# Load the model
model = BertForSequenceClassification.from_pretrained('bert-base-uncased')

# Define the training arguments
training_args = TrainingArguments(
    output_dir='./results',
    num_train_epochs=1,
    per_device_train_batch_size=16,
    warmup_steps=500,
    weight_decay=0.01,
)

# Create the trainer and train
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=train_dataset,
)

trainer.train()

That's it! You have now trained a sentiment analysis model using BERT. This model can classify sentences into positive or negative sentiment. With a bit more work, you can extend this to a multi-class problem, handle larger datasets, and tune the model's hyperparameters to achieve higher accuracy.

This first project should give you a good idea of what it's like to use transformer models in practice. Remember, the key steps are data preparation, model training, and model evaluation. In the next project, we'll delve into a different application of transformer models: text generation. Stay tuned!

7.3 Understanding the BERT Output

When we pass our tokenized inputs through the model, BERT gives us a sequence of hidden-states which is the activations of the last layer of the model. This process is fundamental to the functioning of BERT, as it allows the model to create a representation of the text that is more nuanced and contextualized.

This output is a sequence of contextual word embeddings i.e., each word gets an embedding which depends on the other words in the sentence. This means that the model is able to capture the complex relationships between words in a sentence, and provide a more accurate representation of the meaning of the text. In addition, we get a pooled output which is a summary of the content of the sentence.

This summary is an aggregation of the contextual word embeddings, and provides a higher-level representation of the text that can be used for downstream tasks such as sentiment analysis or information retrieval. Overall, the process of passing tokenized inputs through a BERT model is a powerful tool for natural language processing, allowing for more nuanced and accurate representations of text.

For instance:

from transformers import BertModel

model = BertModel.from_pretrained('bert-base-uncased')
outputs = model(**inputs)
last_hidden_state = outputs.last_hidden_state
pooled_output = outputs.pooler_output
  • last_hidden_state: This is a sequence of hidden states of the last layer of the model. It is a tensor of shape (batch_size, sequence_length, hidden_size). We can use these to get a sequence of contextual word embeddings.
  • pooled_output: This is a pooled representation of the last_hidden_state. It is a tensor of shape (batch_size, hidden_size). This can be used as an embedding for the entire sentence.

We are now equipped with a solid understanding of how to preprocess text data for transformer models, and how to work with their output. This is all the knowledge we need to dive into our first project: Sentiment Analysis with BERT.

Project 1: Sentiment Analysis with BERT

Sentiment Analysis is a classic NLP problem where the goal is to classify text according to the sentiment expressed in it. For instance, the sentence "I love this movie!" expresses a positive sentiment, while "I hate this movie!" expresses a negative sentiment. In this project, we will build a sentiment analysis model using BERT.

Let's start by defining the problem more formally:

Problem Definition

Problem: Classify sentences into their corresponding sentiment. The sentiments could be positive, negative, or neutral.

Data: The data is composed of sentences and their corresponding sentiment labels. For the sake of this example, we'll assume a binary classification task (positive and negative sentiment), but this could easily be extended to a multi-class problem (including neutral sentiment).

Example:

Sentence: "I love this movie!"

Label: Positive

Sentence: "I hate this movie!"

Label: Negative

Data Preparation

The first step in any machine learning project is preparing the data. We will need a labeled dataset composed of sentences and their corresponding sentiment labels. There are many such datasets available publicly, one of which is the IMDB movie reviews dataset.

We can load and preprocess this data using the Hugging Face datasets library:

from datasets import load_dataset

# Load the dataset
dataset = load_dataset("imdb")

# Print a few examples
print(dataset['train'][0])

This will load the IMDB dataset and print out the first training example. Each example consists of a text (the review) and a label (0 or 1, corresponding to negative or positive sentiment).

Model Training

Once we have prepared the data, we can move on to training our model. First, we tokenize our data:

from transformers import BertTokenizerFast

# Load the BERT tokenizer
tokenizer = BertTokenizerFast.from_pretrained('bert-base-uncased')

# Tokenize the data
train_encodings = tokenizer(dataset['train']['text'], truncation=True, padding=True)

Next, we prepare our data for the PyTorch framework:

import torch

# Prepare PyTorch Dataset
class IMDBDataset(torch.utils.data.Dataset):
    def __init__(self, encodings, labels):
        self.encodings = encodings
        self.labels = labels

    def __getitem__(self, idx):
        item = {key: torch.tensor(val[idx]) for key, val in self.encodings.items()}
        item['labels'] = torch.tensor(self.labels[idx])
        return item

    def __len__(self):
        return len(self.labels)

# Create the Dataset
train_dataset = IMDBDataset(train_encodings, dataset['train']['label'])

Finally, we train our model:

from transformers import BertForSequenceClassification, Trainer, TrainingArguments

# Load the model
model = BertForSequenceClassification.from_pretrained('bert-base-uncased')

# Define the training arguments
training_args = TrainingArguments(
    output_dir='./results',
    num_train_epochs=1,
    per_device_train_batch_size=16,
    warmup_steps=500,
    weight_decay=0.01,
)

# Create the trainer and train
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=train_dataset,
)

trainer.train()

That's it! You have now trained a sentiment analysis model using BERT. This model can classify sentences into positive or negative sentiment. With a bit more work, you can extend this to a multi-class problem, handle larger datasets, and tune the model's hyperparameters to achieve higher accuracy.

This first project should give you a good idea of what it's like to use transformer models in practice. Remember, the key steps are data preparation, model training, and model evaluation. In the next project, we'll delve into a different application of transformer models: text generation. Stay tuned!

7.3 Understanding the BERT Output

When we pass our tokenized inputs through the model, BERT gives us a sequence of hidden-states which is the activations of the last layer of the model. This process is fundamental to the functioning of BERT, as it allows the model to create a representation of the text that is more nuanced and contextualized.

This output is a sequence of contextual word embeddings i.e., each word gets an embedding which depends on the other words in the sentence. This means that the model is able to capture the complex relationships between words in a sentence, and provide a more accurate representation of the meaning of the text. In addition, we get a pooled output which is a summary of the content of the sentence.

This summary is an aggregation of the contextual word embeddings, and provides a higher-level representation of the text that can be used for downstream tasks such as sentiment analysis or information retrieval. Overall, the process of passing tokenized inputs through a BERT model is a powerful tool for natural language processing, allowing for more nuanced and accurate representations of text.

For instance:

from transformers import BertModel

model = BertModel.from_pretrained('bert-base-uncased')
outputs = model(**inputs)
last_hidden_state = outputs.last_hidden_state
pooled_output = outputs.pooler_output
  • last_hidden_state: This is a sequence of hidden states of the last layer of the model. It is a tensor of shape (batch_size, sequence_length, hidden_size). We can use these to get a sequence of contextual word embeddings.
  • pooled_output: This is a pooled representation of the last_hidden_state. It is a tensor of shape (batch_size, hidden_size). This can be used as an embedding for the entire sentence.

We are now equipped with a solid understanding of how to preprocess text data for transformer models, and how to work with their output. This is all the knowledge we need to dive into our first project: Sentiment Analysis with BERT.

Project 1: Sentiment Analysis with BERT

Sentiment Analysis is a classic NLP problem where the goal is to classify text according to the sentiment expressed in it. For instance, the sentence "I love this movie!" expresses a positive sentiment, while "I hate this movie!" expresses a negative sentiment. In this project, we will build a sentiment analysis model using BERT.

Let's start by defining the problem more formally:

Problem Definition

Problem: Classify sentences into their corresponding sentiment. The sentiments could be positive, negative, or neutral.

Data: The data is composed of sentences and their corresponding sentiment labels. For the sake of this example, we'll assume a binary classification task (positive and negative sentiment), but this could easily be extended to a multi-class problem (including neutral sentiment).

Example:

Sentence: "I love this movie!"

Label: Positive

Sentence: "I hate this movie!"

Label: Negative

Data Preparation

The first step in any machine learning project is preparing the data. We will need a labeled dataset composed of sentences and their corresponding sentiment labels. There are many such datasets available publicly, one of which is the IMDB movie reviews dataset.

We can load and preprocess this data using the Hugging Face datasets library:

from datasets import load_dataset

# Load the dataset
dataset = load_dataset("imdb")

# Print a few examples
print(dataset['train'][0])

This will load the IMDB dataset and print out the first training example. Each example consists of a text (the review) and a label (0 or 1, corresponding to negative or positive sentiment).

Model Training

Once we have prepared the data, we can move on to training our model. First, we tokenize our data:

from transformers import BertTokenizerFast

# Load the BERT tokenizer
tokenizer = BertTokenizerFast.from_pretrained('bert-base-uncased')

# Tokenize the data
train_encodings = tokenizer(dataset['train']['text'], truncation=True, padding=True)

Next, we prepare our data for the PyTorch framework:

import torch

# Prepare PyTorch Dataset
class IMDBDataset(torch.utils.data.Dataset):
    def __init__(self, encodings, labels):
        self.encodings = encodings
        self.labels = labels

    def __getitem__(self, idx):
        item = {key: torch.tensor(val[idx]) for key, val in self.encodings.items()}
        item['labels'] = torch.tensor(self.labels[idx])
        return item

    def __len__(self):
        return len(self.labels)

# Create the Dataset
train_dataset = IMDBDataset(train_encodings, dataset['train']['label'])

Finally, we train our model:

from transformers import BertForSequenceClassification, Trainer, TrainingArguments

# Load the model
model = BertForSequenceClassification.from_pretrained('bert-base-uncased')

# Define the training arguments
training_args = TrainingArguments(
    output_dir='./results',
    num_train_epochs=1,
    per_device_train_batch_size=16,
    warmup_steps=500,
    weight_decay=0.01,
)

# Create the trainer and train
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=train_dataset,
)

trainer.train()

That's it! You have now trained a sentiment analysis model using BERT. This model can classify sentences into positive or negative sentiment. With a bit more work, you can extend this to a multi-class problem, handle larger datasets, and tune the model's hyperparameters to achieve higher accuracy.

This first project should give you a good idea of what it's like to use transformer models in practice. Remember, the key steps are data preparation, model training, and model evaluation. In the next project, we'll delve into a different application of transformer models: text generation. Stay tuned!

7.3 Understanding the BERT Output

When we pass our tokenized inputs through the model, BERT gives us a sequence of hidden-states which is the activations of the last layer of the model. This process is fundamental to the functioning of BERT, as it allows the model to create a representation of the text that is more nuanced and contextualized.

This output is a sequence of contextual word embeddings i.e., each word gets an embedding which depends on the other words in the sentence. This means that the model is able to capture the complex relationships between words in a sentence, and provide a more accurate representation of the meaning of the text. In addition, we get a pooled output which is a summary of the content of the sentence.

This summary is an aggregation of the contextual word embeddings, and provides a higher-level representation of the text that can be used for downstream tasks such as sentiment analysis or information retrieval. Overall, the process of passing tokenized inputs through a BERT model is a powerful tool for natural language processing, allowing for more nuanced and accurate representations of text.

For instance:

from transformers import BertModel

model = BertModel.from_pretrained('bert-base-uncased')
outputs = model(**inputs)
last_hidden_state = outputs.last_hidden_state
pooled_output = outputs.pooler_output
  • last_hidden_state: This is a sequence of hidden states of the last layer of the model. It is a tensor of shape (batch_size, sequence_length, hidden_size). We can use these to get a sequence of contextual word embeddings.
  • pooled_output: This is a pooled representation of the last_hidden_state. It is a tensor of shape (batch_size, hidden_size). This can be used as an embedding for the entire sentence.

We are now equipped with a solid understanding of how to preprocess text data for transformer models, and how to work with their output. This is all the knowledge we need to dive into our first project: Sentiment Analysis with BERT.

Project 1: Sentiment Analysis with BERT

Sentiment Analysis is a classic NLP problem where the goal is to classify text according to the sentiment expressed in it. For instance, the sentence "I love this movie!" expresses a positive sentiment, while "I hate this movie!" expresses a negative sentiment. In this project, we will build a sentiment analysis model using BERT.

Let's start by defining the problem more formally:

Problem Definition

Problem: Classify sentences into their corresponding sentiment. The sentiments could be positive, negative, or neutral.

Data: The data is composed of sentences and their corresponding sentiment labels. For the sake of this example, we'll assume a binary classification task (positive and negative sentiment), but this could easily be extended to a multi-class problem (including neutral sentiment).

Example:

Sentence: "I love this movie!"

Label: Positive

Sentence: "I hate this movie!"

Label: Negative

Data Preparation

The first step in any machine learning project is preparing the data. We will need a labeled dataset composed of sentences and their corresponding sentiment labels. There are many such datasets available publicly, one of which is the IMDB movie reviews dataset.

We can load and preprocess this data using the Hugging Face datasets library:

from datasets import load_dataset

# Load the dataset
dataset = load_dataset("imdb")

# Print a few examples
print(dataset['train'][0])

This will load the IMDB dataset and print out the first training example. Each example consists of a text (the review) and a label (0 or 1, corresponding to negative or positive sentiment).

Model Training

Once we have prepared the data, we can move on to training our model. First, we tokenize our data:

from transformers import BertTokenizerFast

# Load the BERT tokenizer
tokenizer = BertTokenizerFast.from_pretrained('bert-base-uncased')

# Tokenize the data
train_encodings = tokenizer(dataset['train']['text'], truncation=True, padding=True)

Next, we prepare our data for the PyTorch framework:

import torch

# Prepare PyTorch Dataset
class IMDBDataset(torch.utils.data.Dataset):
    def __init__(self, encodings, labels):
        self.encodings = encodings
        self.labels = labels

    def __getitem__(self, idx):
        item = {key: torch.tensor(val[idx]) for key, val in self.encodings.items()}
        item['labels'] = torch.tensor(self.labels[idx])
        return item

    def __len__(self):
        return len(self.labels)

# Create the Dataset
train_dataset = IMDBDataset(train_encodings, dataset['train']['label'])

Finally, we train our model:

from transformers import BertForSequenceClassification, Trainer, TrainingArguments

# Load the model
model = BertForSequenceClassification.from_pretrained('bert-base-uncased')

# Define the training arguments
training_args = TrainingArguments(
    output_dir='./results',
    num_train_epochs=1,
    per_device_train_batch_size=16,
    warmup_steps=500,
    weight_decay=0.01,
)

# Create the trainer and train
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=train_dataset,
)

trainer.train()

That's it! You have now trained a sentiment analysis model using BERT. This model can classify sentences into positive or negative sentiment. With a bit more work, you can extend this to a multi-class problem, handle larger datasets, and tune the model's hyperparameters to achieve higher accuracy.

This first project should give you a good idea of what it's like to use transformer models in practice. Remember, the key steps are data preparation, model training, and model evaluation. In the next project, we'll delve into a different application of transformer models: text generation. Stay tuned!