How to Find Column Duplicates

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RDG 2014-6-25

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评论： Jos (10584) 2014-6-25

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Suppose:

How can I find the duplicate value and their indices for column 3? Resultant should be: Value: 1,2 Indices: Can be 1,3 --OR-- 1,2,3,4,5.

I tried unique but it returns 5 as well, which is something I don't want.

Gracias.

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Jos (10584) 2014-6-25

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https://ww2.mathworks.cn/matlabcentral/answers/137526-how-to-find-column-duplicates#answer_142401

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X = A{1}
X = X(:,3) % just column 3
[a,i,j] = unique(X)     % find all unique elements
n = histc(j,1:numel(a)) % frequency
tf = n > 1              % Which occur more than once?
required result = a(tf) % select those

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RDG 2014-6-25

Thanks for the prompt reply. What about the indices of those value? (2nd part of the question)

Jos (10584) 2014-6-25

requiredindices = i(tf)

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