MATLAB: How to Find Column Duplicates

duplicatesunique

Suppose:
 A{1}=
  2  3  1  2
  2  1  1  3
  2  3  2  4
  2  5  2  5
  2  6  2  6
  2  2  5  2
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.

Best Answer

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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