Which Data Structure Is Used for Key-Value Pairs?


Angela Bailey

The data structure that is commonly used for key-value pairs is called a dictionary or a map. This data structure allows you to store and retrieve values based on unique keys. In other programming languages, it may be referred to as an associative array or a hash table.

A dictionary is a collection of key-value pairs, where each key is unique and associated with a specific value. The dictionary data structure provides efficient lookup, insertion, and deletion operations.

The key in a dictionary is used to uniquely identify each value. It can be of any data type that supports comparison operations, such as strings, numbers, or even custom objects.

The value in a dictionary can be any object or data type. It can be a simple value like an integer or string, or it can be more complex like another dictionary or a list.

Why Use a Dictionary?

Dictionaries are widely used because they provide fast access to values based on their keys. Unlike arrays or lists where elements are accessed by their index, dictionaries allow you to look up values using meaningful keys.

  • Fast Lookup: Dictionaries use an internal algorithm called hashing to map keys to their corresponding values. This allows for constant-time lookup regardless of the size of the dictionary.
  • Flexible Keys: Dictionaries support various types of keys, allowing you to use strings, numbers, or even custom objects as identifiers.
  • Dynamic Size: Dictionaries can grow and shrink dynamically as new key-value pairs are added or removed.

Implementations of Dictionaries

There are different implementations of dictionaries available in different programming languages:

1. Python – Dictionary

In Python, dictionaries are implemented using a hash table. You can create a dictionary by enclosing key-value pairs in curly braces {} or by using the built-in `dict()` constructor.

# Creating a dictionary
my_dict = {
“name”: “John”,
“age”: 25,
“city”: “New York”

# Accessing values
print(my_dict[“name”]) # Output: John

# Modifying values
my_dict[“age”] = 26

# Adding new key-value pairs
my_dict[“occupation”] = “Developer”

# Removing a key-value pair
del my_dict[“city”]

2. Java – HashMap

In Java, the `HashMap` class is commonly used to implement dictionaries. It uses hashing and chaining to store and retrieve key-value pairs efficiently.

// Import the HashMap class
import java.util.HashMap;

// Creating a HashMap instance
HashMap myMap = new HashMap<>();

// Adding key-value pairs
myMap.put(“apple”, 1);
myMap.put(“banana”, 2);
myMap.put(“cherry”, 3);

// Accessing values
System.out.println(myMap.get(“apple”)); // Output: 1

// Modifying values
myMap.put(“banana”, 4);

// Removing a key-value pair


Dictionaries are essential data structures for storing and retrieving key-value pairs efficiently. They provide fast lookup operations, flexible keys, and dynamic size.

Depending on the programming language, dictionaries may have different names like maps, hash tables, or associative arrays. Understanding how to use dictionaries will greatly enhance your ability to work with key-value data in your programs.

Now that you have learned about dictionaries, you can use them effectively in your programs for efficient storage and retrieval of key-value pairs.

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