⚖️ NumPy vs Python Lists

Understanding the differences between NumPy arrays and Python lists is crucial for effective numerical computing! While both can store sequences of data, they serve very different purposes. NumPy arrays are specifically designed for fast, efficient numerical operations, while Python lists are general-purpose containers.

Let's explore why NumPy arrays are the go-to choice for data science and scientific computing!

import numpy as np

# Same data, different containers
python_list = [1, 2, 3, 4, 5]
numpy_array = np.array([1, 2, 3, 4, 5])

print("Python list:", python_list)
print("NumPy array:", numpy_array)
print()

print("List type:", type(python_list))
print("Array type:", type(numpy_array))
print()

# The magic difference - operations on entire array!
print("Multiply by 2:")
print("List needs loop:", [x * 2 for x in python_list])
print("Array is vectorized:", numpy_array * 2)

🏎️ Performance Comparison

The speed difference between lists and arrays becomes dramatic with larger datasets:

import numpy as np
import time

# Performance comparison with medium-sized data
size = 100000

# Create test data
python_list = list(range(size))
numpy_array = np.arange(size)

print(f"Testing with {size:,} numbers")
print()

# Time list operation
start_time = time.time()
list_result = [x * 2 + 1 for x in python_list]
list_time = time.time() - start_time

# Time array operation  
start_time = time.time()
array_result = numpy_array * 2 + 1
array_time = time.time() - start_time

print(f"List operation time: {list_time:.4f} seconds")
print(f"Array operation time: {array_time:.4f} seconds")
print(f"Array is {list_time/array_time:.1f}x faster!")

📊 Data Type Differences

Lists and arrays handle data types very differently:

import numpy as np

# Lists can mix types
mixed_list = [1, 2.5, "hello", True, [1, 2]]
print("Mixed list:", mixed_list)
print("List allows any types!")
print()

# Arrays require same type
try:
    # This will convert everything to strings
    mixed_array = np.array([1, 2.5, "hello", True])
    print("Mixed array:", mixed_array)
    print("Array dtype:", mixed_array.dtype)
except:
    print("Array creation failed")

print()

# Numeric type promotion
int_list = [1, 2, 3]
mixed_numeric = [1, 2.5, 3]

int_array = np.array(int_list)
float_array = np.array(mixed_numeric)

print("Integer array:", int_array, "dtype:", int_array.dtype)
print("Float array:", float_array, "dtype:", float_array.dtype)

🧮 Mathematical Operations

The way lists and arrays handle math operations is completely different:

import numpy as np

# Sample data
list1 = [1, 2, 3, 4]
list2 = [10, 20, 30, 40]
array1 = np.array([1, 2, 3, 4])
array2 = np.array([10, 20, 30, 40])

print("List 1:", list1)
print("List 2:", list2)
print("Array 1:", array1)
print("Array 2:", array2)
print()

# Addition behaves differently!
print("List addition (concatenation):", list1 + list2)
print("Array addition (element-wise):", array1 + array2)
print()

# Multiplication differences
print("List multiplication (repetition):", list1 * 2)
print("Array multiplication (scaling):", array1 * 2)
print()

# Arrays support element-wise operations
print("Array element-wise operations:")
print("Subtraction:", array2 - array1)
print("Division:", array2 / array1)
print("Power:", array1 ** 2)

📐 Multidimensional Data

Arrays excel at handling multidimensional data like matrices and tensors:

import numpy as np

# 2D data comparison
matrix_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
matrix_array = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

print("Matrix as nested list:")
print(matrix_list)
print()

print("Matrix as NumPy array:")
print(matrix_array)
print()

# Accessing elements
print("Accessing element [1,2]:")
print("List way:", matrix_list[1][2])
print("Array way:", matrix_array[1, 2])
print()

# Operations on entire matrix
print("Add 10 to all elements:")
# List way - need nested loops
list_plus_10 = [[cell + 10 for cell in row] for row in matrix_list]
print("List result:", list_plus_10)

# Array way - vectorized
array_plus_10 = matrix_array + 10
print("Array result:")
print(array_plus_10)

🔍 Memory Usage Comparison

Arrays are much more memory efficient than lists:

import numpy as np
import sys

# Create comparable data structures
size = 1000
python_list = list(range(size))
numpy_array = np.arange(size)

# Calculate memory usage
list_memory = sys.getsizeof(python_list) + sum(sys.getsizeof(item) for item in python_list)
array_memory = numpy_array.nbytes + sys.getsizeof(numpy_array)

print(f"Data size: {size:,} integers")
print(f"List memory: {list_memory:,} bytes")
print(f"Array memory: {array_memory:,} bytes")
print(f"Array uses {list_memory/array_memory:.1f}x less memory!")
print()

# Memory per element
print(f"Memory per element:")
print(f"List: {list_memory/size:.1f} bytes per integer")
print(f"Array: {array_memory/size:.1f} bytes per integer")

🛠️ Functionality Comparison

Compare what you can do with lists vs arrays:

import numpy as np

# Arrays have rich mathematical functionality
data = np.array([1, 4, 9, 16, 25])

print("Original data:", data)
print("Square roots:", np.sqrt(data))
print("Logarithms:", np.log(data))
print("Sine values:", np.sin(data))
print()

# Statistical operations
print("Statistics:")
print(f"Mean: {np.mean(data):.1f}")
print(f"Standard deviation: {np.std(data):.1f}")
print(f"Minimum: {np.min(data)}")
print(f"Maximum: {np.max(data)}")
print()

# These operations would require importing math module 
# and writing loops for Python lists!
print("Lists would need:")
print("import math")
print("sqrt_list = [math.sqrt(x) for x in python_list]")
print("Much more verbose and slower!")

🎯 When to Use Which?

Choose the right tool for the job:

📈 Practical Example: Data Analysis

Let's see arrays in action for a real data analysis task:

import numpy as np

# Simulated daily temperature readings for a month
temperatures = np.array([
    22, 24, 23, 25, 27, 26, 24,  # Week 1
    23, 21, 22, 25, 28, 29, 27,  # Week 2  
    26, 24, 23, 22, 20, 21, 23,  # Week 3
    25, 27, 28, 30, 29, 28, 26   # Week 4
])

print("Temperature Analysis (°C)")
print("=" * 30)
print(f"Temperatures: {temperatures}")
print()

# Easy statistical analysis with arrays
print(f"Average temperature: {np.mean(temperatures):.1f}°C")
print(f"Hottest day: {np.max(temperatures)}°C")
print(f"Coldest day: {np.min(temperatures)}°C")
print(f"Temperature range: {np.max(temperatures) - np.min(temperatures)}°C")
print(f"Standard deviation: {np.std(temperatures):.1f}°C")
print()

# Find days above average
above_average = temperatures > np.mean(temperatures)
hot_days = temperatures[above_average]
print(f"Days above average: {len(hot_days)} days")
print(f"Hot day temperatures: {hot_days}")

# This would be much more complex with Python lists!

🎯 Key Takeaways

🚀 What's Next?

Perfect! Now you understand why NumPy arrays are the foundation of scientific computing in Python. Next, let's explore the properties and attributes that make arrays so powerful and informative.

Continue to: Array Attributes

You're mastering the fundamentals! 🔢⚡

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