INTRODUCTION TO DATA SCIENCE
WFAiS UJ, Informatyka Stosowana I stopień studiów
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This lecture is
based on course by E. Fox and C. Guestrin, Univ of Washington
Classification
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An inteligent restaurant review system
What is a sentiment of the review
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Topic sentiments
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Inteligent restaurant review system
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Core building block
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Inteligent restaurant review system
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Classifier
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Multiclass classifier
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Spam filtering
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Image classification
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Personalized medical diagnosis
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Reading your mind
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Representing classifiers
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Simple threshold classifier
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Simple threshold classifier
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Problems with threshold classifier
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A (linear) classifier
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Scoring a sentence
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Simple linear classifier
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Suppose only two words had non-zero weight
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Decision boundary example
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Decision boundary
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Separates positive & negative predictions
Training a classifier = Learning the weights
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Classification error & accuracy
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What if you ignore the sentence and just guess?
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Is a classifier with 90% accuracy good?
Depends…
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What is a good accuracy?
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Types of mistakes
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True positive
True
negative False negative False
positive
Cost of mistakes
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Confusion matrix: binary classification
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Confusion matrix: multiclass classification
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How much data does a model need to learn?
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Learning curves
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Learning curves
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More complex models tend to have less bias…
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Classification based on bigrams
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How confident is your prediction?
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We have discussed how to
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