Logic for Tokenizing Each Individual Split by Space

Oct 13, 2025 by wbrum.org 132 views

Introduction

Named Entity Recognition (NER) is a fundamental task in natural language processing (NLP) that involves identifying and categorizing named entities in unstructured text into predefined categories such as person, organization, location, etc. Simple Transformers is a popular library for NLP tasks, including NER, that provides a simple and efficient way to train and deploy NER models. In this article, we will explore how Simple Transformers handles split by space predictions for NER models, specifically BERT NER models.

Understanding the `predict` Function

The predict function in Simple Transformers is used to make predictions on a given input text. When using the split_on_space argument, the model predicts the output on a word level basis, which can include subwords. However, the model output is on a token basis, which can be confusing. To understand how the model aggregates the output for each split, we need to dive deeper into the underlying logic.

Tokenization and Encoding

The load_and_cache_examples function in Simple Transformers is responsible for encoding the input text into a format that can be fed into the model. This process involves tokenization, where the input text is split into individual tokens, and encoding, where each token is converted into a numerical representation. The convert_examples_features function is used to perform this encoding.

Model Prediction

Once the input text is encoded, the model predicts the output on a token basis. The model output is a probability distribution over the possible classes for each token. However, since the input text is split by space, the model output needs to be aggregated for each split.

Aggregating Model Output

The _convert_tokens_to_word_logits function is used to convert the token-level model output into word-level logits. This function takes the token-level model output and aggregates it for each split. The aggregation logic is not explicitly stated in the Simple Transformers documentation, but it is likely based on the argmax function, which returns the index of the maximum value in the probability distribution.

Logic for Tokenizing Each Individual Split by Space

To tokenize each individual split by space, the model uses a combination of tokenization and subwording techniques. The input text is first split into individual words, and then each word is further split into subwords using a technique called WordPiece tokenization. The subwords are then used to represent the original word.

High-Level Overview of the Prediction Process

Here is a high-level overview of the prediction process:

Tokenization: The input text is split into individual tokens using a combination of tokenization and subwording techniques.
Encoding: Each token is converted into a numerical representation using the convert_examples_features function.
Model Prediction: The model predicts the output on a token basis, returning a probability distribution over the possible classes for each token.
Aggregation: The token-level model output is aggregated for each split using the _convert_tokens_to_word_logits function.
Prediction: The final prediction is made by taking the argmax of the aggregated model output.

Implementing a Similar Prediction Process

To implement a similar prediction process using an existing token classification model, you can follow these steps:

Tokenization: Split the input text into individual tokens using a combination of tokenization and subwording techniques.
Encoding: Convert each token into a numerical representation using a function similar to convert_examples_features.
Model Prediction: Use the token classification model to predict the output on a token basis, returning a probability distribution over the possible classes for each token.
Aggregation: Aggregate the token-level model output for each split using a function similar to _convert_tokens_to_word_logits.
Prediction: Make the final prediction by taking the argmax of the aggregated model output.

Conclusion

In this article, we explored how Simple Transformers handles split by space predictions for NER models, specifically BERT NER models. We also provided a high-level overview of the prediction process and outlined the steps to implement a similar prediction process using an existing token classification model. By understanding the underlying logic of Simple Transformers, you can develop more efficient and effective NER models for your specific use case.

Code Implementation

Here is a code implementation of the prediction process using an existing token classification model:

import torch
from transformers import AutoTokenizer, AutoModelForTokenClassification

# Load the pre-trained token classification model and tokenizer
model_name = "bert-base-uncased"
tokenizer = AutoTokenizer.from_pretrained(model_name)
model = AutoModelForTokenClassification.from_pretrained(model_name)

# Define a function to tokenize the input text
def tokenize_text(text):
    inputs = tokenizer.encode_plus(
        text,
        add_special_tokens=True,
        max_length=512,
        return_attention_mask=True,
        return_tensors="pt",
    )
    return inputs["input_ids"], inputs["attention_mask"]

# Define a function to encode the input text
def encode_text(input_ids, attention_mask):
    encoded_text = torch.tensor(input_ids)
    attention_mask = torch.tensor(attention_mask)
    return encoded_text, attention_mask

# Define a function to make predictions on the encoded text
def make_predictions(encoded_text, attention_mask):
    outputs = model(encoded_text, attention_mask=attention_mask)
    logits = outputs.logits
    return logits

# Define a function to aggregate the model output for each split
def aggregate_output(logits):
    aggregated_logits = torch.argmax(logits, dim=1)
    return aggregated_logits

# Define a function to make the final prediction
def make_final_prediction(aggregated_logits):
    final_prediction = torch.argmax(aggregated_logits)
    return final_prediction

# Test the prediction process
text = "This is a test sentence."
input_ids, attention_mask = tokenize_text(text)
encoded_text, attention_mask = encode_text(input_ids, attention_mask)
logits = make_predictions(encoded_text, attention_mask)
aggregated_logits = aggregate_output(logits)
final_prediction = make_final_prediction(aggregated_logits)
print(final_prediction)

Q: What is the purpose of the `split_on_space` argument in Simple Transformers?

A: The split_on_space argument in Simple Transformers is used to split the input text into individual words, which can then be processed by the model on a word level basis.

Q: How does Simple Transformers tokenize the input text?

A: Simple Transformers uses a combination of tokenization and subwording techniques to tokenize the input text. The input text is first split into individual words, and then each word is further split into subwords using a technique called WordPiece tokenization.

Q: What is the difference between tokenization and subwording?

A: Tokenization is the process of splitting the input text into individual tokens, such as words or subwords. Subwording is the process of further splitting each token into smaller subwords, which can then be used to represent the original token.

Q: How does Simple Transformers encode the input text?

A: Simple Transformers uses the convert_examples_features function to encode the input text. This function takes the tokenized input text and converts it into a numerical representation that can be fed into the model.

Q: What is the purpose of the `_convert_tokens_to_word_logits` function in Simple Transformers?

A: The _convert_tokens_to_word_logits function in Simple Transformers is used to convert the token-level model output into word-level logits. This function aggregates the token-level model output for each split and returns the final prediction.

Q: How does Simple Transformers make predictions on the encoded text?

A: Simple Transformers uses the make_predictions function to make predictions on the encoded text. This function takes the encoded text and returns the model output, which is a probability distribution over the possible classes for each token.

Q: What is the purpose of the `argmax` function in Simple Transformers?

A: The argmax function in Simple Transformers is used to take the argmax of the model output, which returns the index of the maximum value in the probability distribution. This is used to make the final prediction.

Q: Can I use Simple Transformers to make predictions on text data that is not split by space?

A: Yes, you can use Simple Transformers to make predictions on text data that is not split by space. However, you will need to modify the split_on_space argument to False and use a different tokenization strategy.

Q: How can I implement a similar prediction process using an existing token classification model?

A: You can implement a similar prediction process using an existing token classification model by following the steps outlined in the previous article. This involves tokenizing the input text, encoding the text, making predictions on the encoded text, aggregating the model output, and making the final prediction.

Q: What are some common use cases for Simple Transformers?

A: Simple Transformers is commonly used for named entity recognition (NER), part-of-speech tagging (POS), and sentiment analysis. It can also be used for other NLP tasks such as text classification, question answering, and machine translation.

Q: What are some benefits of using Simple Transformers?

A: Some benefits of using Simple Transformers include its ease of use, flexibility, and high accuracy. It also supports a wide range of pre-trained models and can be used for both English and non-English languages.

Q: What are some limitations of using Simple Transformers?

A: Some limitations of using Simple Transformers include its reliance on pre-trained models, which may not perform well on out-of-distribution data. It also requires a significant amount of computational resources and can be slow for large datasets.