Three spellings of one day
A bakery list holds the dates 02/03/2026, 2 March 2026 and 2026-03-02. They are one day, written three ways.
A computer sees three different pieces of text. Before any analysis, the dates must be changed into one type and one format.
Key words
| Word | What it means | Example |
|---|---|---|
| Convert | To change data from one type to another. | Text "12" to the number 12 |
| Format | The way a value is written down. | Year, then month, then day |
| Type conversion | Changing the kind of a value in code. | int("12") |
| Parse | To read text and pull out its parts in a form a program can use. | Split a date at each slash |
| Currency | A money value, such as pounds and pence. | £12.50 |
| Requirement | What the analysis must achieve. | Total sales by day |
| ISO date | A date written year-month-day, which sorts correctly as text. | 2026-03-02 |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can change money, dates and yes or no values into one consistent type, and check the result.
Starter: what you already know
Have a go
Starter: what you already know
3 questionsHave a go: your answers are marked here and then forgotten. Sign in if you would like your score kept, and to pick up where you left off.Sign in to keep your score
Your answers are marked here and are not kept. A college account keeps every student’s marks.
Worked example: three messy values
| Raw value | Problem | Fixed value |
|---|---|---|
| £12.50 | A pound sign makes it text | 1250 pence, a whole number |
| 02/03/2026 | Day first, in text | 2026-03-02 |
| Y | A letter, not true or false | true |
| Sam | Extra spaces | Sam |
The cells students fill in are left blank in this preview.
Try it: convert in DuckDB
select cast(price as decimal(8,2)) as price,
strptime(day, '%d/%m/%Y')::date as day,
paid = 'Y' as paid
from raw;
-- Try it: add price * 2 as double_price to the list.Try it: convert in Python
text = "£12.50"
clean = text.replace("£", "")
parts = clean.split(".")
pence = int(parts[0]) * 100 + int(parts[1])
print(pence, type(pence))
# Why whole pence? Whole numbers add up exactly. Decimals can drift.
# Try it: change the price to "£0.99" and press Run.