Arrays (up to 3 dimensions), records, lists and tuples

Arrays (of up to 3 dimensions), records, lists, tuples

1.4.2 Data Structures

Data Structures — Note 1 of 3

Candidates should be able to describe what is meant by arrays (up to 3 dimensions), records, lists and tuples. They are expected to be able recognise when they can be used and incorporate them in their programs to store data

What you need to know

Data structures organise related data so it can be processed efficiently. Arrays hold a fixed number of items of the same type; records group related fields of different types; lists are dynamic; tuples are fixed and cannot be changed.

What to know

Key terms

Exam tipCommon mistake

Array: A static (fixed size) data structure holding items of the same data type, accessed by index. OCR arrays are zero-indexed.
A 2D array can be visualised as a table (board[row, col]); a 3D array adds a third index, e.g. sales[shop, month, product].
Static structures (arrays) have a fixed memory size, which can waste space but makes access fast and predictable. Dynamic structures (lists) can grow and shrink but need extra memory to manage.
Record: A data structure that groups related fields, which can have different data types, e.g. a student record with name (string), age (integer) and enrolled (Boolean).
List: A dynamic data structure whose size can change as items are added or removed; items can be of different types in languages like Python.
Tuple: An ordered collection of items that is IMMUTABLE: once created, its items cannot be changed, added or removed.
Exam tip: Choose a structure that suits the data, e.g. a tuple for values that must not change, such as the coordinates of a fixed point.

Code examples

Arrays, records, lists and tuples in Python

python

grid = [[0] * 3 for _ in range(3)]      # 2D array (3 x 3)
grid[1][2] = 5

student = {"name": "Sam", "age": 17, "enrolled": True}   # record

scores = [12, 7, 9]                     # list (dynamic)
scores.append(15)

origin = (0, 0)                         # tuple (immutable)
# origin[0] = 5  would cause an error