kNN-afstandsscore

Zodra de kNN-afstandsmatrix beschikbaar is, kun je de afstandsscore van de naaste buren berekenen door voor elk punt de afstanden tot de naaste buren te middelen.

Grote waarden van de afstandsscore kun je interpreteren als een aanwijzing voor de aanwezigheid van ongebruikelijke of afwijkende punten.

Deze oefening maakt deel uit van de cursus

Introductie tot anomaliedetectie in R

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Oefeninstructies

Bereken de k-nearest neighbor-afstandsscore met de functie rowMeans().
Print de rij-index van het punt met de grootste afstandsscore.

Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Calculate the 5 nearest neighbors distance
wine_nn <- get.knn(wine, k = 5)

# Create score by averaging distances
wine_nnd <- rowMeans(___)

# Print row index of the most anomalous point

Code bewerken en uitvoeren

Deze oefening maakt deel uit van de cursus

Introductie tot anomaliedetectie in R

SkillTag.level.intermediateSkillTag.label

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In this chapter, you'll learn how numerical and graphical summaries can be used to informally assess whether data contain unusual points. You'll use a statistical procedure called Grubbs' test to check whether a point is an outlier, and learn about the Seasonal-Hybrid ESD algorithm, which can help identify outliers when the data are a time series.

Exercise 1: What do we mean when we talk about anomalies?Exercise 2: Recognizing anomaly types Exercise 3: Exploring the river nitrate data Exercise 4: Testing the extremes with Grubbs' test Exercise 5: Visual check of normality Exercise 6: Grubbs' test Exercise 7: Hunting multiple outliers using Grubbs' test Exercise 8: Anomalies in time series Exercise 9: Visual assessment of seasonality Exercise 10: Seasonal Hybrid ESD algorithm Exercise 11: Interpreting Seasonal-Hybrid ESD output Exercise 12: Seasonal-Hybrid ESD versus Grubbs' test

In this chapter, you'll learn how to calculate the k-nearest neighbors distance and the local outlier factor, which are used to construct continuous anomaly scores for each data point when the data have multiple features. You'll learn the difference between local and global anomalies and how the two algorithms can help in each case.

Exercise 1: k-nearest neighbors-afstandsscore Exercise 2: Wijn verkennen Exercise 3: kNN-afstandsmatrix Exercise 4: kNN-afstandsscore

Huidige oefening

Exercise 5: kNN-afstand visualiseren Exercise 6: Features standaardiseren Exercise 7: De kNN-score toevoegen Exercise 8: kNN-afstandsscore visualiseren Exercise 9: Local outlier factor Exercise 10: LOF-berekening Exercise 11: LOF-visualisatie Exercise 12: LOF vs kNN

k-nearest neighbors distance and local outlier factor use the distance or relative density of the nearest neighbors to score each point. In this chapter, you'll explore an alternative tree-based approach called an isolation forest, which is a fast and robust method of detecting anomalies that measures how easily points can be separated by randomly splitting the data into smaller and smaller regions.

Exercise 1: Isolation trees Exercise 2: Fit and predict with an isolation tree Exercise 3: Score interpretation Exercise 4: Isolation forest Exercise 5: Fit an isolation forest Exercise 6: Checking convergence Exercise 7: Visualizing the isolation score Exercise 8: A grid of points Exercise 9: Prediction over a grid Exercise 10: Anomaly contours

You've now been introduced to a few different algorithms for anomaly scoring. In this final chapter, you'll learn to compare the detection performance of the algorithms in instances where labeled anomalies are available. You'll learn to calculate and interpret the precision and recall statistics for an anomaly score, and how to adapt the algorithms so they can accommodate data with categorical features.

Exercise 1: Labeled anomalies Exercise 2: Thyroid data Exercise 3: Visualizing thyroid disease Exercise 4: Anomaly score Exercise 5: Measuring performance Exercise 6: Binarized scores Exercise 7: Cross-tabulate binary scores Exercise 8: Thyroid precision and recall Exercise 9: Working with categorical features Exercise 10: Converting character to factor Exercise 11: Isolation forest with factors Exercise 12: LOF with factors Exercise 13: Wrap-up