Chapter 10: Training, Fine-tuning, and Evaluation of Transformer Models
10.1 Preprocessing Data for Transformers
Welcome to Chapter 10: Training, Fine-tuning, and Evaluation of Transformer Models. This chapter is packed with valuable information that will help you train, fine-tune, and evaluate transformer models for a variety of applications. By the time you finish this chapter, you'll have a solid understanding of how to use transformer models to solve real-world problems.
In the previous chapters, we focused on the theoretical aspects of transformer models and explored their implementation using popular libraries. Now, we're going to delve into the practical aspects of training these models on our own datasets, fine-tuning pre-trained models for specific tasks, and evaluating their performance. This hands-on experience will give you a deeper understanding of how these models work and how to use them effectively.
But before we can start training our models, we need to talk about data preprocessing. This is a crucial step that is often overlooked, but it can have a huge impact on the performance of our models. In this chapter, we'll go over the importance of data preprocessing and show you how to do it correctly. We'll cover techniques like data cleaning, normalization, and feature scaling, and we'll discuss how to handle missing data and deal with outliers.
By the end of this chapter, you'll have a solid foundation in training, fine-tuning, and evaluating transformer models, and you'll know how to preprocess your data to get the best performance out of your models. So let's get started!
Before a dataset can be used to train a transformer model, it needs to be preprocessed. Preprocessing is an essential step in natural language processing, which refers to the use of computers to analyze, understand, and generate human language. In the context of transformer models, preprocessing typically involves three main steps: tokenization, padding, and attention mask creation.
Tokenization involves breaking down the raw text into smaller units, such as words, subwords, or characters. This step is crucial because it allows the transformer model to understand the meaning of individual units and their relationships with other units in the text. Padding is the process of adding extra tokens to the input sequence to ensure that all sequences have the same length.
This is necessary because transformer models require fixed-length input sequences. Finally, attention mask creation is the process of creating a binary mask that indicates which tokens in the input sequence should be attended to by the transformer model and which tokens should be ignored.
In summary, preprocessing is a critical step in preparing a dataset for use with transformer models. The three main steps involved in preprocessing are tokenization, padding, and attention mask creation, which are essential for converting raw text into a format that can be used as input to a transformer model.
Let's dive into each of these steps in more detail:
10.1.1 Tokenization
The first step in preprocessing is tokenization, which is a vital process in natural language processing (NLP) that involves breaking down the input text into smaller pieces, known as tokens. While English and some other languages can be tokenized with a simple space-based tokenizer, many other languages and more complex NLP tasks require subword tokenization algorithms such as Byte-Pair Encoding (BPE) or SentencePiece. These algorithms break words down into smaller, more meaningful units, which can be useful for better capturing the nuances of a language.
When working with transformer models, it is important to use tokenizers that are specific to the model architecture. Fortunately, Hugging Face's Transformers library provides these tokenizers out of the box, making it easy to preprocess text for use with transformer models.
Example:
Here's an example of tokenizing a sentence using BERT's tokenizer:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentence = "Hello, I am learning about transformers!"
tokens = tokenizer.tokenize(sentence)
print(tokens)10.1.2 Padding and Truncation
After tokenization, sentences might be of different lengths, while a model usually expects input sequences to be of a fixed length. This can cause issues during training, as the model may not be able to handle sequences of varying lengths. To address this, we need to ensure all sequences are of the same length.
One way to do this is by truncating the longer sentences. Truncation involves simply chopping off the extra tokens from the end of the sentence beyond a defined maximum length. Another way is by padding the shorter sentences. Padding involves adding a special [PAD] token to the shorter sentences until they match the length of the longest sentence. Both of these techniques can help us ensure that our model receives input sequences of the same length, which can improve its performance during training and inference.
Example:
Again, the tokenizers provided by Hugging Face's Transformers library allow us to do this easily:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Tokenize, pad and truncate
input_ids = tokenizer(sentences, padding='longest', truncation=True, max_length=10, return_tensors='pt')
print(input_ids)10.1.3 Attention Masks
The attention mask is a vital component of the transformer model, which is used in natural language processing tasks such as language translation and text classification. The attention mask is a binary tensor that has the same shape as the input tensor, and its purpose is to indicate which tokens in the input sequence should be attended to by the model and which ones should be ignored.
This is particularly important when dealing with sequences of varying lengths, where padding is often used to make all sequences the same length. The attention mask ensures that the model does not attend to the padded tokens, which would otherwise introduce noise into the model's prediction.
By selectively attending to the relevant tokens, the attention mask allows the model to focus on the most important information in the input sequence, which can lead to more accurate predictions and better performance overall.
Example:
When we called the tokenizer with return_tensors='pt', it also returned attention masks in addition to the input IDs:
print(input_ids['attention_mask'])This is a basic introduction to data preprocessing for transformer models. Each model might have some additional specific requirements, but the general principles remain the same.
The principles covered here should provide a solid understanding of the basics of data preprocessing for transformer models. However, it's important to note that the process of preprocessing can be significantly more complex when dealing with more complex tasks or when working with non-English languages. Here are some points to consider:
- Language-specific tokenization: The tokenization process can greatly vary between languages. Languages that do not use spaces for word separation, like Chinese or Japanese, or languages with complex morphological structures, like Turkish or Finnish, require specific tokenization strategies.
- Handling of special tokens: Many transformer models make use of special tokens. For example, BERT uses
[CLS]and[SEP]tokens to mark the beginning and end of sentences, while GPT-2 uses a special end-of-sentence token. When preprocessing data, it's important to incorporate these special tokens correctly. - Sequence Length: In the padding and truncation section, we defined a maximum sequence length. In practice, it's crucial to choose an appropriate maximum length for your specific task. A too small value might result in losing important information, while a too large value might be computationally inefficient.
- Other preprocessing steps: Depending on the task and the specific dataset, other preprocessing steps might be required, such as lowercasing, removal of special characters, dealing with out-of-vocabulary words, etc.
Here is a more complex example of preprocessing with special tokens and consideration of maximum sequence length:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Define maximum sequence length
max_length = 64
# Tokenize, add special tokens, pad and truncate
input_ids = tokenizer(sentences, padding='max_length', truncation=True, max_length=max_length, add_special_tokens=True, return_tensors='pt')
print(input_ids)10.1 Preprocessing Data for Transformers
Welcome to Chapter 10: Training, Fine-tuning, and Evaluation of Transformer Models. This chapter is packed with valuable information that will help you train, fine-tune, and evaluate transformer models for a variety of applications. By the time you finish this chapter, you'll have a solid understanding of how to use transformer models to solve real-world problems.
In the previous chapters, we focused on the theoretical aspects of transformer models and explored their implementation using popular libraries. Now, we're going to delve into the practical aspects of training these models on our own datasets, fine-tuning pre-trained models for specific tasks, and evaluating their performance. This hands-on experience will give you a deeper understanding of how these models work and how to use them effectively.
But before we can start training our models, we need to talk about data preprocessing. This is a crucial step that is often overlooked, but it can have a huge impact on the performance of our models. In this chapter, we'll go over the importance of data preprocessing and show you how to do it correctly. We'll cover techniques like data cleaning, normalization, and feature scaling, and we'll discuss how to handle missing data and deal with outliers.
By the end of this chapter, you'll have a solid foundation in training, fine-tuning, and evaluating transformer models, and you'll know how to preprocess your data to get the best performance out of your models. So let's get started!
Before a dataset can be used to train a transformer model, it needs to be preprocessed. Preprocessing is an essential step in natural language processing, which refers to the use of computers to analyze, understand, and generate human language. In the context of transformer models, preprocessing typically involves three main steps: tokenization, padding, and attention mask creation.
Tokenization involves breaking down the raw text into smaller units, such as words, subwords, or characters. This step is crucial because it allows the transformer model to understand the meaning of individual units and their relationships with other units in the text. Padding is the process of adding extra tokens to the input sequence to ensure that all sequences have the same length.
This is necessary because transformer models require fixed-length input sequences. Finally, attention mask creation is the process of creating a binary mask that indicates which tokens in the input sequence should be attended to by the transformer model and which tokens should be ignored.
In summary, preprocessing is a critical step in preparing a dataset for use with transformer models. The three main steps involved in preprocessing are tokenization, padding, and attention mask creation, which are essential for converting raw text into a format that can be used as input to a transformer model.
Let's dive into each of these steps in more detail:
10.1.1 Tokenization
The first step in preprocessing is tokenization, which is a vital process in natural language processing (NLP) that involves breaking down the input text into smaller pieces, known as tokens. While English and some other languages can be tokenized with a simple space-based tokenizer, many other languages and more complex NLP tasks require subword tokenization algorithms such as Byte-Pair Encoding (BPE) or SentencePiece. These algorithms break words down into smaller, more meaningful units, which can be useful for better capturing the nuances of a language.
When working with transformer models, it is important to use tokenizers that are specific to the model architecture. Fortunately, Hugging Face's Transformers library provides these tokenizers out of the box, making it easy to preprocess text for use with transformer models.
Example:
Here's an example of tokenizing a sentence using BERT's tokenizer:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentence = "Hello, I am learning about transformers!"
tokens = tokenizer.tokenize(sentence)
print(tokens)10.1.2 Padding and Truncation
After tokenization, sentences might be of different lengths, while a model usually expects input sequences to be of a fixed length. This can cause issues during training, as the model may not be able to handle sequences of varying lengths. To address this, we need to ensure all sequences are of the same length.
One way to do this is by truncating the longer sentences. Truncation involves simply chopping off the extra tokens from the end of the sentence beyond a defined maximum length. Another way is by padding the shorter sentences. Padding involves adding a special [PAD] token to the shorter sentences until they match the length of the longest sentence. Both of these techniques can help us ensure that our model receives input sequences of the same length, which can improve its performance during training and inference.
Example:
Again, the tokenizers provided by Hugging Face's Transformers library allow us to do this easily:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Tokenize, pad and truncate
input_ids = tokenizer(sentences, padding='longest', truncation=True, max_length=10, return_tensors='pt')
print(input_ids)10.1.3 Attention Masks
The attention mask is a vital component of the transformer model, which is used in natural language processing tasks such as language translation and text classification. The attention mask is a binary tensor that has the same shape as the input tensor, and its purpose is to indicate which tokens in the input sequence should be attended to by the model and which ones should be ignored.
This is particularly important when dealing with sequences of varying lengths, where padding is often used to make all sequences the same length. The attention mask ensures that the model does not attend to the padded tokens, which would otherwise introduce noise into the model's prediction.
By selectively attending to the relevant tokens, the attention mask allows the model to focus on the most important information in the input sequence, which can lead to more accurate predictions and better performance overall.
Example:
When we called the tokenizer with return_tensors='pt', it also returned attention masks in addition to the input IDs:
print(input_ids['attention_mask'])This is a basic introduction to data preprocessing for transformer models. Each model might have some additional specific requirements, but the general principles remain the same.
The principles covered here should provide a solid understanding of the basics of data preprocessing for transformer models. However, it's important to note that the process of preprocessing can be significantly more complex when dealing with more complex tasks or when working with non-English languages. Here are some points to consider:
- Language-specific tokenization: The tokenization process can greatly vary between languages. Languages that do not use spaces for word separation, like Chinese or Japanese, or languages with complex morphological structures, like Turkish or Finnish, require specific tokenization strategies.
- Handling of special tokens: Many transformer models make use of special tokens. For example, BERT uses
[CLS]and[SEP]tokens to mark the beginning and end of sentences, while GPT-2 uses a special end-of-sentence token. When preprocessing data, it's important to incorporate these special tokens correctly. - Sequence Length: In the padding and truncation section, we defined a maximum sequence length. In practice, it's crucial to choose an appropriate maximum length for your specific task. A too small value might result in losing important information, while a too large value might be computationally inefficient.
- Other preprocessing steps: Depending on the task and the specific dataset, other preprocessing steps might be required, such as lowercasing, removal of special characters, dealing with out-of-vocabulary words, etc.
Here is a more complex example of preprocessing with special tokens and consideration of maximum sequence length:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Define maximum sequence length
max_length = 64
# Tokenize, add special tokens, pad and truncate
input_ids = tokenizer(sentences, padding='max_length', truncation=True, max_length=max_length, add_special_tokens=True, return_tensors='pt')
print(input_ids)10.1 Preprocessing Data for Transformers
Welcome to Chapter 10: Training, Fine-tuning, and Evaluation of Transformer Models. This chapter is packed with valuable information that will help you train, fine-tune, and evaluate transformer models for a variety of applications. By the time you finish this chapter, you'll have a solid understanding of how to use transformer models to solve real-world problems.
In the previous chapters, we focused on the theoretical aspects of transformer models and explored their implementation using popular libraries. Now, we're going to delve into the practical aspects of training these models on our own datasets, fine-tuning pre-trained models for specific tasks, and evaluating their performance. This hands-on experience will give you a deeper understanding of how these models work and how to use them effectively.
But before we can start training our models, we need to talk about data preprocessing. This is a crucial step that is often overlooked, but it can have a huge impact on the performance of our models. In this chapter, we'll go over the importance of data preprocessing and show you how to do it correctly. We'll cover techniques like data cleaning, normalization, and feature scaling, and we'll discuss how to handle missing data and deal with outliers.
By the end of this chapter, you'll have a solid foundation in training, fine-tuning, and evaluating transformer models, and you'll know how to preprocess your data to get the best performance out of your models. So let's get started!
Before a dataset can be used to train a transformer model, it needs to be preprocessed. Preprocessing is an essential step in natural language processing, which refers to the use of computers to analyze, understand, and generate human language. In the context of transformer models, preprocessing typically involves three main steps: tokenization, padding, and attention mask creation.
Tokenization involves breaking down the raw text into smaller units, such as words, subwords, or characters. This step is crucial because it allows the transformer model to understand the meaning of individual units and their relationships with other units in the text. Padding is the process of adding extra tokens to the input sequence to ensure that all sequences have the same length.
This is necessary because transformer models require fixed-length input sequences. Finally, attention mask creation is the process of creating a binary mask that indicates which tokens in the input sequence should be attended to by the transformer model and which tokens should be ignored.
In summary, preprocessing is a critical step in preparing a dataset for use with transformer models. The three main steps involved in preprocessing are tokenization, padding, and attention mask creation, which are essential for converting raw text into a format that can be used as input to a transformer model.
Let's dive into each of these steps in more detail:
10.1.1 Tokenization
The first step in preprocessing is tokenization, which is a vital process in natural language processing (NLP) that involves breaking down the input text into smaller pieces, known as tokens. While English and some other languages can be tokenized with a simple space-based tokenizer, many other languages and more complex NLP tasks require subword tokenization algorithms such as Byte-Pair Encoding (BPE) or SentencePiece. These algorithms break words down into smaller, more meaningful units, which can be useful for better capturing the nuances of a language.
When working with transformer models, it is important to use tokenizers that are specific to the model architecture. Fortunately, Hugging Face's Transformers library provides these tokenizers out of the box, making it easy to preprocess text for use with transformer models.
Example:
Here's an example of tokenizing a sentence using BERT's tokenizer:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentence = "Hello, I am learning about transformers!"
tokens = tokenizer.tokenize(sentence)
print(tokens)10.1.2 Padding and Truncation
After tokenization, sentences might be of different lengths, while a model usually expects input sequences to be of a fixed length. This can cause issues during training, as the model may not be able to handle sequences of varying lengths. To address this, we need to ensure all sequences are of the same length.
One way to do this is by truncating the longer sentences. Truncation involves simply chopping off the extra tokens from the end of the sentence beyond a defined maximum length. Another way is by padding the shorter sentences. Padding involves adding a special [PAD] token to the shorter sentences until they match the length of the longest sentence. Both of these techniques can help us ensure that our model receives input sequences of the same length, which can improve its performance during training and inference.
Example:
Again, the tokenizers provided by Hugging Face's Transformers library allow us to do this easily:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Tokenize, pad and truncate
input_ids = tokenizer(sentences, padding='longest', truncation=True, max_length=10, return_tensors='pt')
print(input_ids)10.1.3 Attention Masks
The attention mask is a vital component of the transformer model, which is used in natural language processing tasks such as language translation and text classification. The attention mask is a binary tensor that has the same shape as the input tensor, and its purpose is to indicate which tokens in the input sequence should be attended to by the model and which ones should be ignored.
This is particularly important when dealing with sequences of varying lengths, where padding is often used to make all sequences the same length. The attention mask ensures that the model does not attend to the padded tokens, which would otherwise introduce noise into the model's prediction.
By selectively attending to the relevant tokens, the attention mask allows the model to focus on the most important information in the input sequence, which can lead to more accurate predictions and better performance overall.
Example:
When we called the tokenizer with return_tensors='pt', it also returned attention masks in addition to the input IDs:
print(input_ids['attention_mask'])This is a basic introduction to data preprocessing for transformer models. Each model might have some additional specific requirements, but the general principles remain the same.
The principles covered here should provide a solid understanding of the basics of data preprocessing for transformer models. However, it's important to note that the process of preprocessing can be significantly more complex when dealing with more complex tasks or when working with non-English languages. Here are some points to consider:
- Language-specific tokenization: The tokenization process can greatly vary between languages. Languages that do not use spaces for word separation, like Chinese or Japanese, or languages with complex morphological structures, like Turkish or Finnish, require specific tokenization strategies.
- Handling of special tokens: Many transformer models make use of special tokens. For example, BERT uses
[CLS]and[SEP]tokens to mark the beginning and end of sentences, while GPT-2 uses a special end-of-sentence token. When preprocessing data, it's important to incorporate these special tokens correctly. - Sequence Length: In the padding and truncation section, we defined a maximum sequence length. In practice, it's crucial to choose an appropriate maximum length for your specific task. A too small value might result in losing important information, while a too large value might be computationally inefficient.
- Other preprocessing steps: Depending on the task and the specific dataset, other preprocessing steps might be required, such as lowercasing, removal of special characters, dealing with out-of-vocabulary words, etc.
Here is a more complex example of preprocessing with special tokens and consideration of maximum sequence length:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Define maximum sequence length
max_length = 64
# Tokenize, add special tokens, pad and truncate
input_ids = tokenizer(sentences, padding='max_length', truncation=True, max_length=max_length, add_special_tokens=True, return_tensors='pt')
print(input_ids)10.1 Preprocessing Data for Transformers
Welcome to Chapter 10: Training, Fine-tuning, and Evaluation of Transformer Models. This chapter is packed with valuable information that will help you train, fine-tune, and evaluate transformer models for a variety of applications. By the time you finish this chapter, you'll have a solid understanding of how to use transformer models to solve real-world problems.
In the previous chapters, we focused on the theoretical aspects of transformer models and explored their implementation using popular libraries. Now, we're going to delve into the practical aspects of training these models on our own datasets, fine-tuning pre-trained models for specific tasks, and evaluating their performance. This hands-on experience will give you a deeper understanding of how these models work and how to use them effectively.
But before we can start training our models, we need to talk about data preprocessing. This is a crucial step that is often overlooked, but it can have a huge impact on the performance of our models. In this chapter, we'll go over the importance of data preprocessing and show you how to do it correctly. We'll cover techniques like data cleaning, normalization, and feature scaling, and we'll discuss how to handle missing data and deal with outliers.
By the end of this chapter, you'll have a solid foundation in training, fine-tuning, and evaluating transformer models, and you'll know how to preprocess your data to get the best performance out of your models. So let's get started!
Before a dataset can be used to train a transformer model, it needs to be preprocessed. Preprocessing is an essential step in natural language processing, which refers to the use of computers to analyze, understand, and generate human language. In the context of transformer models, preprocessing typically involves three main steps: tokenization, padding, and attention mask creation.
Tokenization involves breaking down the raw text into smaller units, such as words, subwords, or characters. This step is crucial because it allows the transformer model to understand the meaning of individual units and their relationships with other units in the text. Padding is the process of adding extra tokens to the input sequence to ensure that all sequences have the same length.
This is necessary because transformer models require fixed-length input sequences. Finally, attention mask creation is the process of creating a binary mask that indicates which tokens in the input sequence should be attended to by the transformer model and which tokens should be ignored.
In summary, preprocessing is a critical step in preparing a dataset for use with transformer models. The three main steps involved in preprocessing are tokenization, padding, and attention mask creation, which are essential for converting raw text into a format that can be used as input to a transformer model.
Let's dive into each of these steps in more detail:
10.1.1 Tokenization
The first step in preprocessing is tokenization, which is a vital process in natural language processing (NLP) that involves breaking down the input text into smaller pieces, known as tokens. While English and some other languages can be tokenized with a simple space-based tokenizer, many other languages and more complex NLP tasks require subword tokenization algorithms such as Byte-Pair Encoding (BPE) or SentencePiece. These algorithms break words down into smaller, more meaningful units, which can be useful for better capturing the nuances of a language.
When working with transformer models, it is important to use tokenizers that are specific to the model architecture. Fortunately, Hugging Face's Transformers library provides these tokenizers out of the box, making it easy to preprocess text for use with transformer models.
Example:
Here's an example of tokenizing a sentence using BERT's tokenizer:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentence = "Hello, I am learning about transformers!"
tokens = tokenizer.tokenize(sentence)
print(tokens)10.1.2 Padding and Truncation
After tokenization, sentences might be of different lengths, while a model usually expects input sequences to be of a fixed length. This can cause issues during training, as the model may not be able to handle sequences of varying lengths. To address this, we need to ensure all sequences are of the same length.
One way to do this is by truncating the longer sentences. Truncation involves simply chopping off the extra tokens from the end of the sentence beyond a defined maximum length. Another way is by padding the shorter sentences. Padding involves adding a special [PAD] token to the shorter sentences until they match the length of the longest sentence. Both of these techniques can help us ensure that our model receives input sequences of the same length, which can improve its performance during training and inference.
Example:
Again, the tokenizers provided by Hugging Face's Transformers library allow us to do this easily:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Tokenize, pad and truncate
input_ids = tokenizer(sentences, padding='longest', truncation=True, max_length=10, return_tensors='pt')
print(input_ids)10.1.3 Attention Masks
The attention mask is a vital component of the transformer model, which is used in natural language processing tasks such as language translation and text classification. The attention mask is a binary tensor that has the same shape as the input tensor, and its purpose is to indicate which tokens in the input sequence should be attended to by the model and which ones should be ignored.
This is particularly important when dealing with sequences of varying lengths, where padding is often used to make all sequences the same length. The attention mask ensures that the model does not attend to the padded tokens, which would otherwise introduce noise into the model's prediction.
By selectively attending to the relevant tokens, the attention mask allows the model to focus on the most important information in the input sequence, which can lead to more accurate predictions and better performance overall.
Example:
When we called the tokenizer with return_tensors='pt', it also returned attention masks in addition to the input IDs:
print(input_ids['attention_mask'])This is a basic introduction to data preprocessing for transformer models. Each model might have some additional specific requirements, but the general principles remain the same.
The principles covered here should provide a solid understanding of the basics of data preprocessing for transformer models. However, it's important to note that the process of preprocessing can be significantly more complex when dealing with more complex tasks or when working with non-English languages. Here are some points to consider:
- Language-specific tokenization: The tokenization process can greatly vary between languages. Languages that do not use spaces for word separation, like Chinese or Japanese, or languages with complex morphological structures, like Turkish or Finnish, require specific tokenization strategies.
- Handling of special tokens: Many transformer models make use of special tokens. For example, BERT uses
[CLS]and[SEP]tokens to mark the beginning and end of sentences, while GPT-2 uses a special end-of-sentence token. When preprocessing data, it's important to incorporate these special tokens correctly. - Sequence Length: In the padding and truncation section, we defined a maximum sequence length. In practice, it's crucial to choose an appropriate maximum length for your specific task. A too small value might result in losing important information, while a too large value might be computationally inefficient.
- Other preprocessing steps: Depending on the task and the specific dataset, other preprocessing steps might be required, such as lowercasing, removal of special characters, dealing with out-of-vocabulary words, etc.
Here is a more complex example of preprocessing with special tokens and consideration of maximum sequence length:
from transformers import BertTokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
sentences = [
"Hello, I am learning about transformers!",
"This is a shorter sentence."
]
# Define maximum sequence length
max_length = 64
# Tokenize, add special tokens, pad and truncate
input_ids = tokenizer(sentences, padding='max_length', truncation=True, max_length=max_length, add_special_tokens=True, return_tensors='pt')
print(input_ids)