# clustering, matlab, nominal data

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Radoslav Vandzura on 14 Jan 2016
Commented: Tom Lane on 30 Jan 2016
Hello All. I need an advice. I need recommend method of clustering which is suitable for nominal data in Matlab. Could you help me, please? I appreciate every idea. Thank you in advance.

Walter Roberson on 15 Jan 2016

### More Answers (2)

Image Analyst on 15 Jan 2016
Try the Classification Learner app on the Apps tab.
##### 1 CommentShowHide None
Tom Lane on 16 Jan 2016
This could work as a post-processing step to assign new data to classes found from the original data. But classificationLearner would require that you know the clusters (groups) for the original data.

Tom Lane on 16 Jan 2016
For hierarchical clustering, consider using Hamming distance. Here's an example that isn't realistic but that illustrates what to do:
x=randi(3,100,4); % noisy coordinates
x(1:50,5:6) = randi(2,50,2); % try to make 1st 50 points closer
x(51:100,5:6) = 2+randi(2,50,2); % next 50 points different
z = linkage(x,'ave','hamming'); % try average linkage clustering
dendrogram(z,100) % show dendrogram with all points
##### 2 CommentsShowHide 1 older comment
Tom Lane on 30 Jan 2016
You are right that the clustering functions operate on matrices so you would need to convert your data to numbers. The grp2idx function could be helpful. And yes, the Classification Learner app is aimed at classifying data into known groups. Here is a simple example where you can see the Hamming distance between data represented by a three-category variable and a two-category variable.
>> x = [1 1;2 1;3 1;1 2;2 2;2 3];
>> squareform(pdist(x,'hamming'))
ans =
0 0.5000 0.5000 0.5000 1.0000 1.0000
0.5000 0 0.5000 1.0000 0.5000 0.5000
0.5000 0.5000 0 1.0000 1.0000 1.0000
0.5000 1.0000 1.0000 0 0.5000 1.0000
1.0000 0.5000 1.0000 0.5000 0 0.5000
1.0000 0.5000 1.0000 1.0000 0.5000 0

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