Quick method to find duplicates in a matrix?

Hi guys,

Does anybody know a quick way of checking to see which elements of a matrix are duplicates?

Such as:

a = [1,2,3,4,5,5,1,6,7];

Can we have matlab return the indices of all 1's and 5's or return: 1, 5

Thanks!

[José-Luis]

What is an element is repeated more than two times?

Answer 1

[Joseph Cheng]

You can try:

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

There may be some parameters in the unique() function to get exactly what you desire but i don't remember it off hand.

[Dan]

Thanks!

Answer 2

[Azzi Abdelmalek]

a = [1,2,3,4,5,5,1,6,9];
[ii,jj,kk]=unique(a)
out=ii(histc(kk,1:numel(ii))>1)

[Dan]

Thanks as well!