# Questions tagged [clustering]

Clustering is the problem of finding groups of data points (often modelled as nodes in a graph) that are closer to each other than to other points.

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### What exactly is the difference between supervised and unsupervised learning?

I am trying to understand clustering methods. What I I think I understood: In supervised learning, the categories/labels data is assigned to are known before computation. So, the labels, classes or ...
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### Algorithm to separate single contour of glyph into several strokes?

A glyph contour contains points set {p}, a point contains tuple (x,y,on_curve). Now, think about this need, converting contour of glyph X, for example, into to two contour parts or two strokes, point ...
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### How to map points in high-dimensional space into dense grid in lower-dimensional space?

A formal description of the problem: Given a set $P$ of $n^k$ points in $d$ dimensional space, what algorithm can I use to find a mapping between them and points on a $n \times n \times n...$ grid in ...
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### Document clustering for summarization

I am curious as to what steps one would reasonably need to take to perform an extraction-based text summarizer. I've taken a look at some papers I've found on Google such as this one, which explains ...
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### How to calculate IV, EV and optimal k for K-means?

Could someone explain how to calculate the following 3 evaluative properties: Intercluster Variability (IV) - How different are the data points within the same cluster Extracluster Variability (EV) - ...
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### What happens when you don't use a metric in k-means?

K-means is a clustering algorithm which works like this: ...
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### Visualize Graph Clusters

I am working on my thesis which involves using ant based techniques for graph clustering. I am testing the algorithm currently and I was wondering if there is a way that I can visualize the clusters ...
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### sum of squared distances from mean equals all-pairs sum of square distances?

In this variance based k-clustering paper they claim that for a cluster with S points: $$|S|\sum_{i \in S}{\|x_i-\bar{x}\|^2} = \sum_{a,b \in S,\ a<b}{\|x_a-x_b\|^2}\,.$$ Why is that? can you ...
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### Is there a well-known algorithm for arranging inputs according to their category?

Background: (I’m a complete beginner in computer science in general, so I do apologise if my question is not formulated in a sensible way. E.g. I have avoided technicalities in formulating my ...
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### Subspace clustering with random transformation

One approach for clustering a high dimensional dataset is to use linear transformation, and the most common approaches are PCA and random projection (where random projection arises from the Johnson-...
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### Algorithms / heuristics for a distributed sorting problem

The setting: There's a cluster of $k$ computers (= nodes). For simplicity, assume their hardware is identical. The network topology can be complicated, but let's simplify and assume it's a clique ...
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