MATLAB: Finding duplicates

unique

A=[ 1 1 2 2 3 3 3];
unique(A)=[1 2 3]; but I want to find the duplicates that are not the first occurrence. i.e x=[2 4 6 7]; I typed help unique but I couldn't figure out if I and J reported by this function helps with my purpose.I know that I can program it but i want to be as efficient as possible in my codes to reduce the running time.

Best Answer

Here is one way:
[uniqueA i j] = unique(A,'first');
indexToDupes = find(not(ismember(1:numel(A),i)))
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