Sets

Introduction

Sets are unordered collections of unique elements. They are useful for membership testing and eliminating duplicates.

Creating Sets

# Basic set
fruits = {"apple", "banana", "cherry"}

# From list (removes duplicates)
nums = set([1, 2, 2, 3, 3, 3])  # {1, 2, 3}

# Empty set (not {})
empty = set()

Set Operations

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

# Union
print(a | b)      # {1, 2, 3, 4, 5, 6}
print(a.union(b))

# Intersection
print(a & b)      # {3, 4}
print(a.intersection(b))

# Difference
print(a - b)      # {1, 2}
print(a.difference(b))

# Symmetric difference
print(a ^ b)      # {1, 2, 5, 6}

Set Methods

s = {1, 2, 3}

s.add(4)          # Add element
s.remove(2)      # Remove (raises error if not found)
s.discard(5)      # Remove (no error)
s.pop()           # Remove and return arbitrary element
s.clear()         # Empty the set

Practice Problems

1. Find common elements in two lists
2. Remove all duplicates from a list
3. Check if one set is subset of another
4. Find elements in first list but not in second
5. Implement set operations for given data