cs-108 — The Sensor Dropout
| Field | Value |
|---|---|
| id | cs-108 |
| difficulty | Advanced |
| topics | anomalies, time series |
| lecture | lecture-27 |
| estimated time | 5-minute attempt + 10-minute discussion |
| prerequisites | functions, dictionaries, and earlier algorithmic patterns |
| objective | design the algorithm, verify it on edges, and argue correctness or trade-offs |
| solution | held by the instructor; discussed after the attempt |
Problem
Temperature sensor with gaps and spikes. Distinguish dropout vs anomaly, impute or flag, and show how each choice changes a downstream average.
Your deliverable is the stated assumptions, the gap rule (missing vs zero vs delayed) made precise, and one record where the rule choice changes the conclusion. If the problem is ambiguous anywhere, state the assumption you are making and carry on — a stated assumption is part of a good answer.
Examples
- Input: temps: [12, 12.5, 13, None, 47, 12.8, None, 13]
- Output: None = dropout (impute or flag, do NOT average over silently); 47 = spike (anomaly vs real heatwave - policy needed)
Solve for the worked instance first. Then ask what would change if one number, name, or condition were replaced by something stranger.
What to notice
- Distinguish GAPS (no data) from OUTLIERS (unlikely data) - they get different treatments.
- Writing the rules IS the solution; code is transcription.
- Every assumption is a place where two good answers can differ.
Discussion starter
After the solution is revealed, the class spends five minutes on this prompt: "Which assumption would you attack first if you had to argue the other side?"
Constraints and assumptions
- Difficulty: Advanced (functions, dictionaries, and algorithmic reasoning assumed).
- Topics: anomalies, time series.
- Classroom-scale inputs unless the problem says otherwise.
- Time-box: about five minutes for a defensible plan; a complete solution may take longer and that is expected - state where you would resume.
- Optional stretch (not required): describe an alternative approach and say when it beats the obvious one.
Hints and extension
- First nudge: identify the pattern the worked instance uses before computing anything.
- If stuck after three minutes, write the input/output line you expect and trace the smallest example by hand.
- After the reveal, attempt the extension below before the next lecture.
- Extension challenge: Draft the audit trail paragraph a reviewer would need to trust your cleaning.