A small analytics example processes visitor IDs recorded for several visits.
What You Need to Understand
Counting unique visitors requires stable visitor identifiers, not simply counting page loads. A set stores one entry per unique identifier in the processed data.
When to Use It
A small analytics example processes visitor IDs recorded for several visits.
Step-by-Step Python Example
visitor_ids = ["u101", "u202", "u101", "u303"]
unique_visitor_ids = set(visitor_ids)
print("Visits:", len(visitor_ids))
print("Unique IDs:", len(unique_visitor_ids))How the Example Works
Four events are present, but only three distinct IDs occurred.
Example Output
Visits: 4
Unique IDs: 3
3 2A Second Example
Compare this smaller variation with the main example, then experiment with your own values.
events = [101, 102, 101]
print(len(events), len(set(events)))Important Behavior and Edge Cases
This technique only counts distinct recorded identifiers, not actual people. Do not infer unique humans from unreliable IDs or store personal data without appropriate privacy controls.
Try It Yourself
Add another visit by an existing ID and observe which count changes.
Common Beginner Mistakes
- This technique only counts distinct recorded identifiers, not actual people. Do not infer unique humans from unreliable IDs or store personal data without appropriate privacy controls.
- Depending on set iteration order or using a set when duplicates and original positions must be preserved.
Key Takeaways
- Counting unique visitors requires stable visitor identifiers, not simply counting page loads.
- Four events are present, but only three distinct IDs occurred.
- This technique only counts distinct recorded identifiers, not actual people.