PCA Usage and Components

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Your question is PCA Usage and Components. Take a moment with it on the right.

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Problem

Why PCA? Where did you apply it? How many components did you select?

Asked in the Amazon R2 technical interview stage. This is a follow-up on applying Principal Component Analysis within a binary classification pipeline. Explain the motivation, placement, preprocessing requirements, component-selection method, and how you verified that PCA improved the system rather than merely reducing dimensionality.

Address:

When PCA is appropriate and when it is harmful.
How you would fit and serve PCA without training-serving skew.
How you would select and validate the number of components.
What metrics and failure modes you would monitor.