Single- and Multi-dimensional Arrays

AQA 4.2.2 — Arrays

Retrieval: Sequence 3's functions took single values as parameters (a name, a score); arrays let a single variable hold a whole collection of values instead - the natural next step once one value at a time stops being enough.

An array is a fixed-size, ordered collection where every element is accessed by an index. AQA's specification (and exam pseudocode) treats arrays as their own concept, distinct from more advanced Python-specific structures — in Python, a list is used to model an array.

scores = [72, 85, 91, 68, 77]
print(scores[0])     # 72 - first element (index 0)
print(scores[-1])    # 77 - last element
print(len(scores))   # 5

Two-dimensional arrays

A 2D array is an array of arrays — useful for grids, seating plans, or timetables.

seating_plan = [
    ["Aisha", "Tom", "Priya"],
    ["Liam", "Sofia", "Omar"],
]
print(seating_plan[0][1])   # "Tom" - row 0, column 1

Strengths and limitations

Strengths: O(1) direct access by index; simple, predictable memory layout. Limitations: fixed size in many languages (Python lists resize dynamically, but AQA's theoretical array model doesn't); inserting/removing in the middle requires shifting elements — O(n).

Common mistake

Because a Python list resizes automatically, it's easy to assume "arrays" are just as flexible in every language and in AQA's theoretical model — they aren't. If an exam question specifies a fixed-size array, assume operations like inserting into the middle require shifting every element after it, which is why understanding an array's limitations (not just its Python convenience) matters.

Worked example — a seating plan manager

def find_student(seating_plan, name):
    for row_index, row in enumerate(seating_plan):
        for col_index, student in enumerate(row):
            if student == name:
                return row_index, col_index
    return None

position = find_student(seating_plan, "Sofia")
print(position)   # (1, 1)

Challenge

Create a 2D array representing a weekly timetable (5 days × 5 periods) and write a function that returns the lesson at a given day and period.