🎪 Sets and Unique Values — Collections Without Duplicates

Sets automatically prevent duplicates and excel at checking membership and finding unique items.

🎯 Creating Sets

A set stores unique values in curly braces, with no specific order.

# Create a set
colors = {"red", "green", "blue"}

# Set from a list (removes duplicates)
numbers = [1, 2, 2, 3, 3, 3, 4]
unique_numbers = set(numbers)
print(unique_numbers)  # {1, 2, 3, 4}

# Empty set (note: {} is an empty dict, not a set)
empty_set = set()

💡 Why Sets Are Useful

Sets are perfect for:

• **Removing duplicates** from data

• **Checking membership** (is X in this collection?)

• **Finding unique items** across datasets

# Automatically removes duplicates
votes = ["Alice", "Bob", "Alice", "Carol", "Bob", "Alice"]
unique_voters = set(votes)
print(unique_voters)  # {'Bob', 'Alice', 'Carol'}
print(len(unique_voters))  # 3

🎨 Real-World Example: Tracking Website Visitors

# Track unique visitors throughout the day
visitors = {"alice", "bob", "carol", "alice", "bob", "david"}

# Convert list to set for uniqueness
visitor_list = ["alice", "bob", "carol", "alice", "bob", "david"]
unique_visitors = set(visitor_list)

print(f"Total visits: {len(visitor_list)}")  # 6
print(f"Unique visitors: {len(unique_visitors)}")  # 4
print(f"Who visited: {unique_visitors}")

📊 Set Methods for Basic Use

🔑 Key Takeaways

• ✅ Sets store only unique values

• ✅ Perfect for removing duplicates

• ✅ Unordered—no index access

• ✅ Fast membership checking with `in`

• ✅ Use for comparing collections

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