NLP Basics Skill

Transform unstructured text into structured insights.

Quick Start

from transformers import AutoTokenizer, AutoModel
import torch

# Load model and tokenizer
tokenizer = AutoTokenizer.from_pretrained('bert-base-uncased')
model = AutoModel.from_pretrained('bert-base-uncased')

# Tokenize
text = "Machine learning is transforming industries."
inputs = tokenizer(text, return_tensors='pt', padding=True, truncation=True)

# Get embeddings
with torch.no_grad():
    outputs = model(**inputs)
    embeddings = outputs.last_hidden_state.mean(dim=1)  # [CLS] pooling

print(f"Embedding shape: {embeddings.shape}")

Key Topics

1. Text Preprocessing

import re
from nltk.tokenize import word_tokenize
from nltk.corpus import stopwords
from nltk.stem import WordNetLemmatizer

class TextPreprocessor:
    def __init__(self):
        self.lemmatizer = WordNetLemmatizer()
        self.stop_words = set(stopwords.words('english'))

    def clean(self, text):
        # Lowercase
        text = text.lower()
        # Remove URLs
        text = re.sub(r'http\S+', '', text)
        # Remove special chars
        text = re.sub(r'[^\w\s]', '', text)
        # Tokenize and filter
        tokens = word_tokenize(text)
        tokens = [self.lemmatizer.lemmatize(t) for t in tokens
                  if t not in self.stop_words]
        return ' '.join(tokens)

2. Word Embeddings

Type	Model	Use Case
Static	Word2Vec, GloVe	Simple, fast
Contextual	BERT, RoBERTa	SOTA accuracy
Sentence	all-MiniLM	Similarity, search

from sentence_transformers import SentenceTransformer

# Sentence embeddings
model = SentenceTransformer('all-MiniLM-L6-v2')
embeddings = model.encode(['Hello world', 'Hi there'])

# Similarity
from sklearn.metrics.pairwise import cosine_similarity
similarity = cosine_similarity([embeddings[0]], [embeddings[1]])[0][0]

3. Text Classification

from transformers import AutoTokenizer, AutoModelForSequenceClassification
from transformers import Trainer, TrainingArguments

# Load pretrained model
model_name = 'bert-base-uncased'
tokenizer = AutoTokenizer.from_pretrained(model_name)
model = AutoModelForSequenceClassification.from_pretrained(
    model_name, num_labels=2
)

# Training arguments
training_args = TrainingArguments(
    output_dir='./results',
    num_train_epochs=3,
    per_device_train_batch_size=16,
    evaluation_strategy='epoch',
    save_strategy='epoch',
    load_best_model_at_end=True
)

# Train
trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=train_dataset,
    eval_dataset=eval_dataset
)
trainer.train()

4. Named Entity Recognition

from transformers import pipeline

# NER pipeline
ner = pipeline('ner', aggregation_strategy='simple')

text = "Apple Inc. was founded by Steve Jobs in Cupertino, California."
entities = ner(text)

for entity in entities:
    print(f"{entity['word']}: {entity['entity_group']} ({entity['score']:.2f})")

5. Semantic Search

from sentence_transformers import SentenceTransformer
import numpy as np

class SemanticSearch:
    def __init__(self, model_name='all-MiniLM-L6-v2'):
        self.model = SentenceTransformer(model_name)
        self.corpus_embeddings = None
        self.corpus = None

    def index(self, documents):
        self.corpus = documents
        self.corpus_embeddings = self.model.encode(documents)

    def search(self, query, top_k=5):
        query_embedding = self.model.encode([query])[0]
        scores = np.dot(self.corpus_embeddings, query_embedding)
        top_indices = np.argsort(scores)[-top_k:][::-1]
        return [(self.corpus[i], scores[i]) for i in top_indices]

Best Practices

DO

• Use pretrained models
• Fine-tune on domain data
• Handle tokenization edge cases
• Batch process for efficiency
• Cache embeddings

DON'T

• Don't ignore text preprocessing
• Don't use large models for simple tasks
• Don't fine-tune without validation
• Don't skip error analysis

Exercises

Exercise 1: Sentiment Analysis

# TODO: Fine-tune BERT for sentiment classification
# Use the IMDB dataset

Exercise 2: Semantic Search

# TODO: Build a semantic search engine
# Index 1000 documents and search by query

Unit Test Template

import pytest

def test_preprocessing():
    """Test text preprocessing."""
    preprocessor = TextPreprocessor()
    text = "Hello World! Visit https://example.com"

    cleaned = preprocessor.clean(text)

    assert 'http' not in cleaned
    assert cleaned.islower()

def test_embeddings_shape():
    """Test embedding dimensions."""
    model = SentenceTransformer('all-MiniLM-L6-v2')
    embeddings = model.encode(['test'])

    assert embeddings.shape == (1, 384)

Troubleshooting

Problem	Cause	Solution
OOV tokens	Rare words	Use subword tokenization
Slow inference	Large model	Use distilled model
Poor accuracy	Small dataset	Data augmentation
Memory error	Long sequences	Reduce max_length

Related Resources

• Agent: 05-nlp
• Previous: deep-learning
• Next: computer-vision
• Docs: HuggingFace

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Version: 1.4.0 | Status: Production Ready