Mapping and Set Types.md

Mapping and Set Types

Table of Contents

• Dictionaries and Sets
  • Dictionaries
  • Sets
• Dictionary Methods
• Set Operations
• Dictionaries VS Sets

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Dictionaries and Sets

Dictionaries

A dictionary is a collection of key-value pairs, where each unique key maps to a specific value. Dictionaries are defined using curly braces {} with each item as a key: value pair. Keys are immutable (like strings, numbers, or tuples) and must be unique, while values can be of any data type and can be duplicated.

Syntax Example:

# Creating a dictionary
my_dict = {"name": "Alice", "age": 25, "city": "New York"}

Sets

A set is an unordered collection of unique items. Sets are also defined using curly braces {} with individual elements separated by commas. Sets automatically remove any duplicate items and are commonly used for mathematical operations.

Syntax Example:

# Creating a set
my_set = {1, 2, 3, 4, 5}

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Dictionary Methods

Dictionaries offer several methods for accessing, updating, and managing key-value pairs:

• get(): Retrieves the value associated with a specified key. If the key does not exist, it returns None (or a specified default value).

  my_dict.get("name")  # Output: "Alice"
  my_dict.get("salary", "Not found")  # Output: "Not found"

• update(): Adds key-value pairs from another dictionary or an iterable of key-value pairs. It updates values of existing keys or adds new pairs.

  my_dict.update({"age": 26, "job": "Engineer"})

• keys(): Returns a view object containing all keys in the dictionary.

  my_dict.keys()  # Output: dict_keys(['name', 'age', 'city', 'job'])

• values(): Returns a view object containing all values in the dictionary.

  my_dict.values()  # Output: dict_values(['Alice', 26, 'New York', 'Engineer'])

• items(): Returns a view object containing all key-value pairs as tuples.

  my_dict.items()  # Output: dict_items([('name', 'Alice'), ('age', 26), ('city', 'New York'), ('job', 'Engineer')])

• pop(): Removes the specified key and returns its value. Raises an error if the key is not found (unless a default value is specified).

  my_dict.pop("city")  # Removes 'city' key and returns its value "New York"

• clear(): Removes all items from the dictionary.

  my_dict.pop("city")  # Removes 'city' key and returns its value "New York"

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Set Operations

Sets provide various mathematical operations to compare and manipulate sets:

• union() (|): Combines all unique elements from two or more sets.

  set_a = {1, 2, 3}
  set_b = {3, 4, 5}
  set_a.union(set_b)  # Output: {1, 2, 3, 4, 5}

• intersection() (&): Returns only the elements that are common to both sets.

  set_a.intersection(set_b)  # Output: {3}

• difference() (-): Returns the elements in the first set that are not in the second set.

  set_a.difference(set_b)  # Output: {1, 2}

• symmetric_difference() (^): Returns the elements that are in either of the sets but not in both.

  set_a.symmetric_difference(set_b)  # Output: {1, 2, 4, 5}

• add(): Adds an element to the set.

  my_set.add(6)  # Adds 6 to the set

• remove() and discard(): Removes an element from the set. remove() raises an error if the element doesn’t exist, while discard() does not.

  my_set.remove(6)  # Removes 6 from the set

• issubset() and issuperset(): Checks if a set is a subset or superset of another set.

  set_a.issubset({1, 2, 3, 4})  # Output: True

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Dictionaries VS Sets

Here’s a table comparing dictionaries and sets with their unique features and use cases:

Feature	Dictionaries	Sets
Definition	Collection of key-value pairs	Unordered collection of unique elements
Syntax	{key: value, ...}	{element1, element2, ...}
Data Access	Accessed by keys (my_dict["key"])	Accessed by elements; supports membership testing (in)
Mutability	Mutable (can add/remove key-value pairs)	Mutable (can add/remove elements)
Use Case	Quick lookups, storing data with unique keys	Set operations (union, intersection), membership tests, story a collection of unique items
Examples	Storing configuration settings, counting items	Eliminating duplicates, mathematical set operations