Day27: Confusion Analyzer

Ai Models From Scratch Beginners Edition ~2 min read 60 min hands-on

Confusion Matrix Deep Dive

Build a production-grade multi-class confusion matrix engine from scratch
using only NumPy. No sklearn. No Keras. Every metric is traceable to a
single array operation.

Quick Start

bash

Open http://localhost:8501 in your browser.

Lifecycle Commands

File Structure

Code

The Central Insight

accuracy = 0.97 can be a lie.

If 97% of your samples belong to class 0 and your model predicts
class 0 for everything, accuracy is 0.97 and macro-F1 is ≈ 0.32.

The confusion matrix is the only tool that shows you where the model
is failing, which classes are confused with which, and what kind
of error (FP vs FN) dominates.

The Key Function

Open model.py and find build_confusion_matrix().
The entire lesson is these two lines:

python

Homework

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