🟪 1-Minute Summary

Clustering is unsupervised learning that groups similar data points together without predefined labels. Common algorithms: K-Means (fast, needs K), Hierarchical (dendrogram, no K needed), DBSCAN (density-based, finds arbitrary shapes). Use cases: customer segmentation, anomaly detection, data exploration. Unlike supervised learning, there’s no “correct” answer - evaluate with silhouette score, elbow method, domain knowledge.


🟦 Core Notes (Must-Know)

What is Clustering?

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Supervised vs Unsupervised Learning

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Common Clustering Algorithms

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Use Cases

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Evaluation Metrics

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🟨 Interview Triggers (What Interviewers Actually Test)

Common Interview Questions

  1. “When would you use clustering vs classification?”

    • [Answer: Clustering when no labels, classification when you have labels]
  2. “How do you evaluate a clustering model?”

    • [Answer: Silhouette score, elbow method, business validation]
  3. “Name 3 clustering algorithms and when to use each”

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🟥 Common Mistakes (Traps to Avoid)

Mistake 1: Not scaling features before clustering

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Mistake 2: Using accuracy for clustering

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🟩 Mini Example (Quick Application)

Scenario

[Customer segmentation example]

Solution

from sklearn.cluster import KMeans
from sklearn.preprocessing import StandardScaler

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