Machine Learning System Design Interview, issue 17, Dec 3, 2025
The Data Leakage Trap
Senior Machine Learning Engineer interview at Google DeepMind, and the interviewer asks:
“How do you handle these missing values before we start training?”
The train-fit/test-transform discipline every ML engineer must know before touching a real pipeline.
The full answer, with the mechanism and the arithmetic, is for paid subscribers on Substack.