Fundamentals of Programming II Overview of Collections Computer Science 112 Fundamentals of Programming II Overview of Collections

Why Collections? Some programs need a container to manage several data objects You’ve used lists, tuples, and dictionaries in Python There are other types of collections as well

What Is a Collection? A collection is a container for zero or more data objects A collection tracks its own size and resizing is automatic A collection comes with built-in operations for access, insertions, removals, etc. Details of the underlying data structures and operations are hidden in the implementation, so we ignore them

Built-in Python Collections String Tuple List Set Dictionary

Basic Categories of Collections Linear Hierarchical Graph Unordered

Linear Collections List Stack Queue Priority Queue 0 1 2 D1 D2 D3 0 1 2 D1 D2 D3 Elements are ordered by position Each element except the first has a unique predecessor Each element except the last has a unique successor

Linear Collections List Stack Queue Priority Queue 0 1 2 D1 D2 D3 0 1 2 D1 D2 D3 Lists allow accesses, replacements, insertions, and removals at any position

Linear Collections List Stack Queue Priority Queue 0 1 2 D1 D2 D3 0 1 2 D1 D2 D3 Stacks allow accesses, insertions and removals at one end only

Linear Collections List Stack Queue Priority Queue 0 1 2 D1 D2 D3 0 1 2 D1 D2 D3 Queues allow insertions at one end and removals and accesses at the other end

Linear Collections List Stack Queue Priority Queue 0 1 2 D1 D2 D3 0 1 2 D1 D2 D3 Priority queues sort elements by priority, but elements with equal priority are added and removed in queue-like order

Hierarchical Collections Binary tree General tree Binary search tree Heap D2 D1 D3 Each element except the root has a unique predecessor Each can have zero or more successors

Graph Collections Undirected graph Directed graph D1 D2 D3 D4 D5 Each element can have zero or more predecessors Each can have zero or more successors

Unordered Collections Bag Set Dictionary D1 D2 D3 D4 D5 No notion of position from the user’s perspective We can visit all the objects with a for loop

Sorted Collections Sorted Set Sorted Dictionary D1 D2 D3 D4 D5 The elements are not ordered by position, but they are ordered by content (ascending order)

Aspects of a Collection Formal properties (what it is and what you can do with it – as expressed in its interface) Implementations – array-based, link-based, etc. Performance characteristics – space/time tradeoffs of different implementations

Basic Types of Operations Create a collection: list(), list(aCollection) Obtain the string representation: str(aCollection) Obtain the number of items currently in the collection: len(aCollection)

Basic Types of Operations Test an item for membership: item in aCollection Iterate through the items: for item in aCollection: . . . Concatenate two collections (of the same type): aCollection1 + aCollection2 Test for equality: aCollection == anObject

Basic Types of Operations Make the collection empty: aCollection.clear() Add an item: aCollection.add(item) Remove an item: aCollection.remove(item)

Searching, Sorting, and Complexity Analysis Chapter 3 For Monday Searching, Sorting, and Complexity Analysis Chapter 3