22-2. Hash Maps

Hash Maps are used to find detailed information about something. In the implementation below, people are stored in a Hash Map. A person can be looked up using a person’s unique social security number (the Hash Map key), and then we can see that person’s name (the Hash Map value).

class SimpleHashMap:
    def __init__(self, size=100):
        self.size = size
        self.buckets = [[] for _ in range(size)]  # A list of buckets, each is a list (to handle collisions)

def hash_function(self, key):
        # Sum only the numerical values of the key, ignoring non-numeric characters
        numeric_sum = sum(int(char) for char in key if char.isdigit())
        return numeric_sum % 10  # Perform modulo 10 on the sum

def put(self, key, value):
        # Add or update a key-value pair
        index = self.hash_function(key)
        bucket = self.buckets[index]
        for i, (k, v) in enumerate(bucket):
            if k == key:
                bucket[i] = (key, value)  # Update existing key
                return
        bucket.append((key, value))  # Add new key-value pair if not found

def get(self, key):
        # Retrieve a value by key
        index = self.hash_function(key)
        bucket = self.buckets[index]
        for k, v in bucket:
            if k == key:
                return v
        return None  # Key not found

def remove(self, key):
        # Remove a key-value pair
        index = self.hash_function(key)
        bucket = self.buckets[index]
        for i, (k, v) in enumerate(bucket):
            if k == key:
                del bucket[i]  # Remove the key-value pair
                return

def print_map(self):
        # Print all key-value pairs in the hash map
        print("Hash Map Contents:")
        for index, bucket in enumerate(self.buckets):
            print(f"Bucket {index}: {bucket}")

# Creating the Hash Map from the simulation
hash_map = SimpleHashMap(size=10)

# Adding some entries
hash_map.put("123-4567", "Charlotte")
hash_map.put("123-4568", "Thomas")
hash_map.put("123-4569", "Jens")
hash_map.put("123-4570", "Peter")
hash_map.put("123-4571", "Lisa")
hash_map.put("123-4672", "Adele")
hash_map.put("123-4573", "Michaela")
hash_map.put("123-6574", "Bob")

hash_map.print_map()

print("\nName associated with '123-4570':", hash_map.get("123-4570"))

print("Updating the name for '123-4570' to 'James'")
hash_map.put("123-4570","James")

print("Name associated with '123-4570':", hash_map.get("123-4570"))

#Python

Output:

It is easier to understand how Hash Maps work if you first have a look at the two previous pages about Hash Tables and Hash Sets. It is also important to understand the meaning of the words below.

Entry: Consists of a key and a value, forming a key-value pair.
Key: Unique for each entry in the Hash Map. Used to generate a hash code determining the entry's bucket in the Hash Map. This ensures that every entry can be efficiently located.
Hash Code: A number generated from an entry's key, to determine what bucket that Hash Map entry belongs to.
Bucket: A Hash Map consists of many such buckets, or containers, to store entries.
Value: Can be nearly any kind of information, like name, birth date, and address of a person. The value can be many different kinds of information combined.

Last updated: April 23, 2025

Python Programming

22-2. Hash Maps