Number of clusters, beyond two dimensions?

[Pacharapol Withayasakpunt]

If two dimensions, it can be as simple as scatter plot, and by eyeballs, but beyond two?

I understand there is elbow method, but how to automate?

Also, I can use DIANA or AGNES, but how to infer number of clusters from dendrogram?

[Pimphen Charoen]

Good questions! Let me ask you a little bit further (and your peers are also very welcome to discuss!).

You are right. For two dimensions, we can simply visualise this in a scatter plot. Do you think how many dimensions we can do visualisation? and when we have many dimensions, is there a way to do so?

Based on the dendrograms from our iris example, can you make a good guess at which cut-off point on the tree can be used to infer a number of clusters and why? Is this the same guess between dendrograms generated from DIANA and AGNES?

For Elbow method, we are going to add R commands for generating the plot in a bit (in section 1.6). Thanks for letting us know!

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