How to aggregate list of dictionaries

Introduction

This tutorial explores comprehensive techniques for aggregating lists of dictionaries in Python, providing developers with powerful strategies to efficiently process and transform complex data structures. By mastering these methods, programmers can simplify data manipulation tasks and write more concise, readable code.

Skills Graph

Dictionary Lists Basics

What is a Dictionary List?

A dictionary list is a powerful data structure in Python that consists of multiple dictionaries stored within a single list. It allows you to represent complex, structured data with multiple entries, each containing key-value pairs.

Basic Structure and Creation

## Creating a list of dictionaries
students = [
    {"name": "Alice", "age": 22, "grade": "A"},
    {"name": "Bob", "age": 21, "grade": "B"},
    {"name": "Charlie", "age": 23, "grade": "A"}
]

Key Characteristics

Common Operations

Data Types in Dictionary Lists

Dictionary lists can contain various data types:

• Strings
• Numbers
• Lists
• Nested dictionaries
• Mixed types

Example in LabEx Python Environment

## Practical example of dictionary list
products = [
    {"id": 1, "name": "Laptop", "price": 1000},
    {"id": 2, "name": "Smartphone", "price": 500},
    {"id": 3, "name": "Tablet", "price": 300}
]

## Iterating through the list
for product in products:
    print(f"Product: {product['name']}, Price: ${product['price']}")

This foundational understanding sets the stage for more advanced dictionary list manipulation and aggregation techniques.

Data Aggregation Methods

Overview of Aggregation Techniques

Aggregating data in lists of dictionaries involves combining, summarizing, and transforming data using various Python methods and techniques.

Key Aggregation Methods

1. Using sum() for Numeric Aggregation

## Summing numeric values
sales_data = [
    {"product": "Laptop", "price": 1000},
    {"product": "Phone", "price": 500},
    {"product": "Tablet", "price": 300}
]

total_sales = sum(item['price'] for item in sales_data)
print(f"Total Sales: ${total_sales}")

2. Filtering Data with list comprehension

## Filtering high-value products
high_value_products = [
    item for item in sales_data if item['price'] > 500
]

3. Grouping Data with collections.defaultdict

from collections import defaultdict

## Grouping products by price range
def categorize_products(products):
    product_groups = defaultdict(list)
    for product in products:
        if product['price'] < 500:
            product_groups['low_price'].append(product)
        elif 500 <= product['price'] < 1000:
            product_groups['medium_price'].append(product)
        else:
            product_groups['high_price'].append(product)
    return product_groups

4. Aggregation Methods Comparison

5. Advanced Aggregation with functools.reduce()

from functools import reduce

## Complex aggregation using reduce
def complex_aggregation(data):
    return reduce(
        lambda acc, item: acc + item['price'] * item.get('quantity', 1),
        data,
        0
    )

Best Practices in LabEx Python Environment

• Use list comprehensions for simple transformations
• Leverage collections module for complex grouping
• Choose appropriate aggregation method based on data structure
• Consider performance for large datasets

Error Handling and Validation

def safe_aggregation(data, key):
    try:
        return sum(item.get(key, 0) for item in data)
    except (TypeError, ValueError) as e:
        print(f"Aggregation error: {e}")
        return None

This comprehensive overview provides multiple strategies for effectively aggregating data in lists of dictionaries, catering to various use cases and complexity levels.

Practical Aggregation Examples

1. Sales Data Analysis

sales_data = [
    {"product": "Laptop", "category": "Electronics", "price": 1000, "quantity": 5},
    {"product": "Phone", "category": "Electronics", "price": 500, "quantity": 10},
    {"product": "Book", "category": "Literature", "price": 20, "quantity": 50}
]

## Total revenue calculation
def calculate_total_revenue(data):
    return sum(item['price'] * item['quantity'] for item in data)

## Category-wise revenue
def category_revenue_breakdown(data):
    category_revenue = {}
    for item in data:
        category = item['category']
        revenue = item['price'] * item['quantity']
        category_revenue[category] = category_revenue.get(category, 0) + revenue
    return category_revenue

2. Student Performance Tracking

students = [
    {"name": "Alice", "math": 85, "science": 90, "english": 88},
    {"name": "Bob", "math": 75, "science": 80, "english": 82},
    {"name": "Charlie", "math": 95, "science": 92, "english": 90}
]

## Calculate average scores
def calculate_subject_averages(students):
    return {
        "math": sum(student['math'] for student in students) / len(students),
        "science": sum(student['science'] for student in students) / len(students),
        "english": sum(student['english'] for student in students) / len(students)
    }

## Find top performers
def find_top_performers(students, subject, top_n=2):
    return sorted(students, key=lambda x: x[subject], reverse=True)[:top_n]

3. Inventory Management

inventory = [
    {"name": "Shirt", "price": 25, "quantity": 100},
    {"name": "Pants", "price": 50, "quantity": 75},
    {"name": "Shoes", "price": 80, "quantity": 50}
]

## Identify low stock items
def find_low_stock_items(inventory, threshold=60):
    return [item for item in inventory if item['quantity'] < threshold]

## Calculate total inventory value
def calculate_inventory_value(inventory):
    return sum(item['price'] * item['quantity'] for item in inventory)

4. Advanced Data Transformation

def transform_and_aggregate(data, transformation_func, aggregation_func):
    transformed_data = [transformation_func(item) for item in data]
    return aggregation_func(transformed_data)

## Example usage in LabEx Python environment
def normalize_price(item):
    return item['price'] / 100

def total_normalized_value(normalized_prices):
    return sum(normalized_prices)

5. Error-Robust Aggregation

def safe_aggregation(data, key, default_value=0):
    try:
        return sum(item.get(key, default_value) for item in data)
    except Exception as e:
        print(f"Aggregation error: {e}")
        return None

Key Takeaways

• Use list comprehensions for concise transformations
• Leverage dictionary methods for flexible aggregations
• Implement error handling for robust data processing
• Choose appropriate aggregation techniques based on data structure

This comprehensive guide demonstrates practical approaches to aggregating and analyzing data in lists of dictionaries, showcasing versatility and efficiency in Python data manipulation.

Summary

Python offers multiple approaches to aggregate list of dictionaries, including using built-in functions, list comprehensions, and specialized libraries like pandas. Understanding these techniques empowers developers to handle complex data transformations with ease, improving code efficiency and readability in various programming scenarios.