K-means clustering for one class classification
The K-means algorithm has the capacity of retrieving which are the "boundaries" your data has for knowing the only-class, is possible that you don't find the only-class boundaries to be the same boundaries your k-means algorithm found. This is the risk of comparing k-means with the one class classification: Clustering can be looking different things from one class classification.
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How to perform model selection for One-Class Classification?