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Prompt Engineering

Full Guide on LLM Synthetic Data Generation




Synthetic data generation using LLM

Large Language Models (LLMs) are powerful tools not just for generating human-like text, but also for creating high-quality synthetic data. This capability is changing how we approach AI development, particularly in scenarios where real-world data is scarce, expensive, or privacy-sensitive. In this comprehensive guide, we'll explore LLM-driven synthetic data generation, diving deep into its methods, applications, and best practices.

Introduction to Synthetic Data Generation with LLMs

Synthetic data generation using LLMs involves leveraging these advanced AI models to create artificial datasets that mimic real-world data. This approach offers several advantages:

  1. Cost-effectiveness: Generating synthetic data is often cheaper than collecting and annotating real-world data.
  2. Privacy protection: Synthetic data can be created without exposing sensitive information.
  3. Scalability: LLMs can generate vast amounts of diverse data quickly.
  4. Customization: Data can be tailored to specific use cases or scenarios.

Let's start by understanding the basic process of synthetic data generation using LLMs:

from transformers import AutoTokenizer, AutoModelForCausalLM
# Load a pre-trained LLM
model_name = "gpt2-large"
tokenizer = AutoTokenizer.from_pretrained(model_name)
model = AutoModelForCausalLM.from_pretrained(model_name)
# Define a prompt for synthetic data generation
prompt = "Generate a customer review for a smartphone:"
# Generate synthetic data
input_ids = tokenizer.encode(prompt, return_tensors="pt")
output = model.generate(input_ids, max_length=100, num_return_sequences=1)
# Decode and print the generated text
synthetic_review = tokenizer.decode(output[0], skip_special_tokens=True)

This simple example demonstrates how an LLM can be used to generate synthetic customer reviews. However, the real power of LLM-driven synthetic data generation lies in more sophisticated techniques and applications.

2. Advanced Techniques for Synthetic Data Generation

2.1 Prompt Engineering

Prompt engineering is crucial for guiding LLMs to generate high-quality, relevant synthetic data. By carefully crafting prompts, we can control various aspects of the generated data, such as style, content, and format.

Example of a more sophisticated prompt:

prompt = """
Generate a detailed customer review for a smartphone with the following characteristics:
- Brand: {brand}
- Model: {model}
- Key features: {features}
- Rating: {rating}/5 stars
The review should be between 50-100 words and include both positive and negative aspects.
brands = ["Apple", "Samsung", "Google", "OnePlus"]
models = ["iPhone 13 Pro", "Galaxy S21", "Pixel 6", "9 Pro"]
features = ["5G, OLED display, Triple camera", "120Hz refresh rate, 8K video", "AI-powered camera, 5G", "Fast charging, 120Hz display"]
ratings = [4, 3, 5, 4]
# Generate multiple reviews
for brand, model, feature, rating in zip(brands, models, features, ratings):
filled_prompt = prompt.format(brand=brand, model=model, features=feature, rating=rating)
input_ids = tokenizer.encode(filled_prompt, return_tensors="pt")
output = model.generate(input_ids, max_length=200, num_return_sequences=1)
synthetic_review = tokenizer.decode(output[0], skip_special_tokens=True)
print(f"Review for {brand} {model}:\n{synthetic_review}\n")

This approach allows for more controlled and diverse synthetic data generation, tailored to specific scenarios or product types.

2.2 Few-Shot Learning

Few-shot learning involves providing the LLM with a few examples of the desired output format and style. This technique can significantly improve the quality and consistency of generated data.

few_shot_prompt = """
Generate a customer support conversation between an agent (A) and a customer (C) about a product issue. Follow this format:
C: Hello, I'm having trouble with my new headphones. The right earbud isn't working.
A: I'm sorry to hear that. Can you tell me which model of headphones you have?
C: It's the SoundMax Pro 3000.
A: Thank you. Have you tried resetting the headphones by placing them in the charging case for 10 seconds?
C: Yes, I tried that, but it didn't help.
A: I see. Let's try a firmware update. Can you please go to our website and download the latest firmware?
Now generate a new conversation about a different product issue:
C: Hi, I just received my new smartwatch, but it won't turn on.
# Generate the conversation
input_ids = tokenizer.encode(few_shot_prompt, return_tensors="pt")
output = model.generate(input_ids, max_length=500, num_return_sequences=1)
synthetic_conversation = tokenizer.decode(output[0], skip_special_tokens=True)

This approach helps the LLM understand the desired conversation structure and style, resulting in more realistic synthetic customer support interactions.

2.3 Conditional Generation

Conditional generation allows us to control specific attributes of the generated data. This is particularly useful when we need to create diverse datasets with certain controlled characteristics.

from transformers import GPT2LMHeadModel, GPT2Tokenizer
import torch
model = GPT2LMHeadModel.from_pretrained("gpt2-medium")
tokenizer = GPT2Tokenizer.from_pretrained("gpt2-medium")
def generate_conditional_text(prompt, condition, max_length=100):
    input_ids = tokenizer.encode(prompt, return_tensors="pt")
    attention_mask = torch.ones(input_ids.shape, dtype=torch.long, device=input_ids.device)
    # Encode the condition
    condition_ids = tokenizer.encode(condition, add_special_tokens=False, return_tensors="pt")
    # Concatenate condition with input_ids
    input_ids =[condition_ids, input_ids], dim=-1)
    attention_mask =[torch.ones(condition_ids.shape, dtype=torch.long, device=condition_ids.device), attention_mask], dim=-1)
    output = model.generate(input_ids, attention_mask=attention_mask, max_length=max_length, num_return_sequences=1, no_repeat_ngram_size=2, do_sample=True, top_k=50, top_p=0.95, temperature=0.7)
    return tokenizer.decode(output[0], skip_special_tokens=True)
# Generate product descriptions with different conditions
conditions = ["Luxury", "Budget-friendly", "Eco-friendly", "High-tech"]
prompt = "Describe a backpack:"
for condition in conditions:
description = generate_conditional_text(prompt, condition)
print(f"{condition} backpack description:\n{description}\n")

This technique allows us to generate diverse synthetic data while maintaining control over specific attributes, ensuring that the generated dataset covers a wide range of scenarios or product types.

Applications of LLM-Generated Synthetic Data

Training Data Augmentation

One of the most powerful applications of LLM-generated synthetic data is augmenting existing training datasets. This is particularly useful in scenarios where real-world data is limited or expensive to obtain.

import pandas as pd
from sklearn.model_selection import train_test_split
from transformers import pipeline
# Load a small real-world dataset
real_data = pd.read_csv("small_product_reviews.csv")
# Split the data
train_data, test_data = train_test_split(real_data, test_size=0.2, random_state=42)
# Initialize the text generation pipeline
generator = pipeline("text-generation", model="gpt2-medium")
def augment_dataset(data, num_synthetic_samples):
    synthetic_data = []
    for _, row in data.iterrows():
        prompt = f"Generate a product review similar to: {row['review']}\nNew review:"
        synthetic_review = generator(prompt, max_length=100, num_return_sequences=1)[0]['generated_text']
        synthetic_data.append({'review': synthetic_review,'sentiment': row['sentiment'] # Assuming the sentiment is preserved})
        if len(synthetic_data) >= num_synthetic_samples:
    return pd.DataFrame(synthetic_data)
# Generate synthetic data
synthetic_train_data = augment_dataset(train_data, num_synthetic_samples=len(train_data))
# Combine real and synthetic data
augmented_train_data = pd.concat([train_data, synthetic_train_data], ignore_index=True)
print(f"Original training data size: {len(train_data)}")
print(f"Augmented training data size: {len(augmented_train_data)}")

This approach can significantly increase the size and diversity of your training dataset, potentially improving the performance and robustness of your machine learning models.

Challenges and Best Practices

While LLM-driven synthetic data generation offers numerous benefits, it also comes with challenges:

  1. Quality Control: Ensure the generated data is of high quality and relevant to your use case. Implement rigorous validation processes.
  2. Bias Mitigation: LLMs can inherit and amplify biases present in their training data. Be aware of this and implement bias detection and mitigation strategies.
  3. Diversity: Ensure your synthetic dataset is diverse and representative of real-world scenarios.
  4. Consistency: Maintain consistency in the generated data, especially when creating large datasets.
  5. Ethical Considerations: Be mindful of ethical implications, especially when generating synthetic data that mimics sensitive or personal information.

Best practices for LLM-driven synthetic data generation:

  1. Iterative Refinement: Continuously refine your prompts and generation techniques based on the quality of the output.
  2. Hybrid Approaches: Combine LLM-generated data with real-world data for optimal results.
  3. Validation: Implement robust validation processes to ensure the quality and relevance of generated data.
  4. Documentation: Maintain clear documentation of your synthetic data generation process for transparency and reproducibility.
  5. Ethical Guidelines: Develop and adhere to ethical guidelines for synthetic data generation and use.


LLM-driven synthetic data generation is a powerful technique that is transforming how we approach data-centric AI development. By leveraging the capabilities of advanced language models, we can create diverse, high-quality datasets that fuel innovation across various domains. As the technology continues to evolve, it promises to unlock new possibilities in AI research and application development, while addressing critical challenges related to data scarcity and privacy.

As we move forward, it's crucial to approach synthetic data generation with a balanced perspective, leveraging its benefits while being mindful of its limitations and ethical implications. With careful implementation and continuous refinement, LLM-driven synthetic data generation has the potential to accelerate AI progress and open up new frontiers in machine learning and data science.

I have spent the past five years immersing myself in the fascinating world of Machine Learning and Deep Learning. My passion and expertise have led me to contribute to over 50 diverse software engineering projects, with a particular focus on AI/ML. My ongoing curiosity has also drawn me toward Natural Language Processing, a field I am eager to explore further.