Data structures

Learning outcomes

• Practice to use classes for expression
• Practice to use classes for type safety
• Practice to use composition for a 'has-a' relationship

Why?

You want to model the real world. The real world consists out of things. You need to convert those things into code.

You want to use data structures.

Good data structures

Good data structures:

• Increase expressiveness
• Bundles data that belongs together
• Ensures correct state of the program

Good example data structures are built-in data structures.

Discussion

• Structures increase expressiveness of code
• The design of data structures has implications
• Structures are useful to bundle data
• It is rare that structures match the real world

structure versus class

Parameter	structure	class
Python keyword	class	class
R object type	S3 class	S4, R5, R6
All states are valid	Yes	No
Maintains a valid state	No	Yes
Example	A number for an x coordinate	A string for a DNA sequence
Invalid when	Never	Sequence holds an invalid nucleotide letter