100% satisfaction guarantee Immediately available after payment Both online and in PDF No strings attached
logo-home
Summary Machine Learning $3.21
Add to cart

Summary

Summary Machine Learning

 150 views  5 purchases
  • Course
  • Institution

Summary of all the lectures of Machine Learning. It contains all the relevant material needed for the final exam.

Preview 4 out of 38  pages

  • December 5, 2023
  • 38
  • 2023/2024
  • Summary
avatar-seller
Summary Machine Learning

Lecture 1 – Introduction to Machine Learning

What is machine learning (ML) about?
 ML is about automation of problem solving.
 It is the study of computer algorithms that improve automatically through experience.
 Involves becoming better at a task T based on some experience E with respect to some
performance measure P
 Examples: spam detection, movie recommendation, speech recognition, credit risk analysis,
autonomous driving and medical diagnosis.

What does it involve?
 ML may involve a notion of generalization. Is it safe to assume that current observations can
be generalized to future observations?
 ML should be generalizable – should perform on unseen data / representative for real world
domain.
 Labeled data, objective, optimization algorithm (models), features/representations (columns),
and assumptions are some critical components.

Different types of learning
 Supervised learning: annotated/labelled dataset / ground truth
o Classification: discrete variable - predicting the price of a house
o Regression: continuous variable - spam detection
 Unsupervised learning: unlabeled dataset
o Clustering, association mining - customer segmentation, recommendation
 Semi supervised learning (only a portion of the data is labeled) - text classification
 Reinforcement learning: based on rewarding desired behaviors and/or punishing undesired
ones. (involves a feedback loop) - self driving car

Example - SPAM versus non-Spam
 Binary classification problem




Learning process
 Find examples of SPAM and non-SPAM
 Come up with a learning algorithm
 A learning algorithm infers rules from examples: If (A or B or C) and not D, then SPAM
 These rules can then be applied to new data (emails)

Learning algorithms

, See several different learning algorithms
 Implement simple 2-3 simple ones from scratch in Python
 Learn about Python libraries for ML (scikit-learn)
 How to apply them to real-world problems

Machine Learning – Examples
 Recognize handwritten numbers and letters
 Recognize faces in photos
 Determine whether text expresses positive, negative or no opinion
 Guess person’s age based on a sample of writing
 Flag suspicious credit-card transactions
 Recommend books and movies to users based on their own and others’ purchase history
 Recognize and label mentions of people’s or organization names in text

Types of learning problems: Regression
 Response: a (real) number
 Predict person’s age, predict price of a stock, predict student’s score on exam
 In regression, the response variable is predicted using a set of predictors that are believed to
have an influence on the response variable.

Types of learning problems: Binary classification
 Response: Yes/No answer
 Detect SPAM
 Predict polarity of product review: positive vs negative

Types of learning problems: Multiclass classification
Response: one of a finite set of options
 Classify newspaper article as
o politics, sports, science, technology, health, finance
 Detect species based on photo
o Passer domesticus, Calidris alba, Streptopelia decaocto, Corvus corax, …

Types of learning problems: Multilabel classification
Response: a finite set of Yes/No answers
 Assign songs to one or more genres
o rock, pop, metal
o hip-hop, rap
o jazz, blues
o rock, punk

Types of learning problems: Autonomous behavior
 Input: measurements from sensors – camera, microphone, radar, accelerometer,. . .
 Response: instructions for actuators – steering, accelerator, brake,

How well is the algorithm learning?
 Evaluation: Choose a baseline, choose a metric, compare!

, different tasks, different metrics

Predicting age – Regression
 Mean absolute error – the average (absolute) difference between true value and predicted
value (yn true value (ground truth), ^y n predicted value) - fails to punish large errors in
prediction as all errors are treated equally.


 Mean squared error – the average square of the difference between true value and predicted
value - more sensitive to outliers as the square amplifies the impact of large deviations.



Predicting spam - Classification


 Drawback: does not work well on imbalanced data. If the data is imbalanced the accuracy
will naturally be high.

Classification
Wrong classification
 False positive (FP) – Flagged as SPAM, but not non-SPAM
 False negative (FN) – Not flagged, but is SPAM
 False positives are a bigger issue for this problem! In the medical field this is the other way
around (False negative are the bigger issue). Minimizing one of the two depends thus on the
problem at hand.
Correct classification
 True positive (TP): Spam classified as spam
 True negative (TN): Not-spam classified as not-spam
Summarized in a confusion matrix (image on the right)
 Confusion matrix can be appended with more decision
classes.

Precision and Recall
 Metrics which focus on one kind of mistake. These are better for imbalanced data (together
with F1-score.
 Precision (positive predictive value (PPV)) – what fraction of flagged emails
were real SPAMs?
 Recall (sensitivity, hit rate, or true positive rate (TPR)) – what fraction of
real SPAMs were flagged?
 Specificity, selectivity or true negative rate (TNR) (usage not common)

Fβ-score
 F1 – score (F-measure): harmonic mean between precision and recall a kind
of average

,  Parameter β quantifies how much more we care about recall than precision,
when it is greater than 1, that means, recall is weighted more, when it is
smaller than 1, that means precision is weighted more.

Macro-average
 Precision and recall are usually calculated per decision class. Micro and
macro average are ways to aggregate the measures.
 Precision true positives over labeled positives; Recall, true positives over
actual positives. ((1), (2), (3), (4),(5)) represent the five data points.)
 Compute precision and recall per-class, and average: ex:

 Rare classes have the same impact as frequent classes (not ideal).
 Macro F1-Score is the harmonic mean of Macro-Precision and Macro-Recall.

Micro-average
 Micro averaging treats the entire set of data as an aggregate result, and calculates 1 metric
rather than k metrics that get averaged together.


 In micro averaging, we calculate one aggregate result for the entire data set (for precision and
recall and use these micro averaged precision and recall for the micro averaged F1).
 Micro-Average Precision and Recall are just the same values when there is one label, so is the
Micro Average F1-Score, and the accuracy.

How to find ^f ( x ) : A solution workflow
 Best outcome we can hope for: ^f ( x ) = f (x) for all x. Ideally, we would like ^f ( x ) such that a
loss between f(x) and ^f ( x ) is minimized, i.e., L( ^f ( x ) , f (x)) is small.
 The cost (average loss plus possibly a regularization term) in case of regression can be MSE
or MAE, computed over all values of x
 Problem 1 We do not have all values of x and f (x) (might not represent the whole population)
 Problem 2 We do not know how f (x) looks like (distribution)
 Compute loss on the data we have (empirical risk minimization) for MAE:



How to find ^f ( x )
 If ^f ( x ) = θx + c we assume a linear relationship


 For a more complex relationship, a polynomial function can also be used
 Choose a power p ^f ( x ) = c + θ1x + θ2x2 + . . . θpxp Higher p implies higher degree of
freedom/flexibility (and more fitted to the data -> risk of overfitting)



Changing p: overfitting / underfitting

The benefits of buying summaries with Stuvia:

Guaranteed quality through customer reviews

Guaranteed quality through customer reviews

Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.

Quick and easy check-out

Quick and easy check-out

You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.

Focus on what matters

Focus on what matters

Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!

Frequently asked questions

What do I get when I buy this document?

You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.

Satisfaction guarantee: how does it work?

Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.

Who am I buying these notes from?

Stuvia is a marketplace, so you are not buying this document from us, but from seller bascrypto. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy these notes for $3.21. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

52510 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy study notes for 14 years now

Start selling
$3.21  5x  sold
  • (0)
Add to cart
Added