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Can someone give me some scenario where it's better to use clustering (unsupervised classification) than supervised classification such as SVM ? I mean in a case where you know the data labels/classes.

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It largely depends on what the goals of your analysis are. Labels only become labels when you decide that they are a feature of interest! In one context a dataset may be labelled but in another it could easily be considered unlabelled.

Consider a dataset containing information about apples with the features being height, width and price. Now a shopkeeper might be interested in a supervised regression approach treating price as the label (and width and height as predictors), in order to predict how much he should sell new apples for. On the other hand, an apple farmer might be interested in applying a clustering technique to the full dataset with all three variables (with no particular label variable) in order to figure out how many varieties (Granny Smith etc.) are contained in the dataset. Clearly, the latter is a case where clustering would be more appropriate.

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  • $\begingroup$ What is the best approach when you want to know if the features that you use to classify/cluster are accurate. For example, you have 2 classes of subjects, healthy and sick and as features you have: blood pressure, weight, heart pain. and you want to know if those features are able to separate the 2 groups in your database. In that cas it doesn't matter if you use supervised or unsupervised classification, no? $\endgroup$ – learneRS Aug 20 '18 at 11:55
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    $\begingroup$ That sounds to me like the general supervised learning problem statement and unfortunately there is no simple answer, in fact the field of machine learning is pretty much based on this question. This short post that I recently wrote might help clear up the supervised vs unsupervised question distinction for you (in fact please let me know how helpful it is!) alanjeffares.wordpress.com/2018/07/24/test $\endgroup$ – Seraf Fej Aug 20 '18 at 13:12
  • $\begingroup$ good vulgarization. I just wished I had some references that show some cases where unsupervised classification is more adapted than supervised classification. thank you $\endgroup$ – learneRS Aug 21 '18 at 10:45

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