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pink
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detect same value

Asked by pink
on 10 Jun 2011
how do I detect on the elements of a (:, 1) there is the same value?
a=[1 34;
2 33;
2 45;
3 32;
4 65;
4 99;
5 11;
1 33;
6 22]

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1 Answer

Answer by Walter Roberson
on 10 Jun 2011
 Accepted Answer

u = unique(a(:,1));
if length(u) ~= size(a,1)
%there were duplicates
end
If you want to find out which are equal to which,
bsxfun(@eq, a(:,1), a(:,1).'))
and that will return a logical matrix in which for row r, column c is set if a(r) == a(c)

  2 Comments

M M
on 6 Mar 2013
How would you isolate the duplicated values? So I would know which values are duplicated and use them for another purpose? (The opposite of the unique function)
setdiff(V, unique(V)) %for vector V, results are in sorted order
or
T = bsxfun(@eq, V(:), V(:).'); %for vector V
sum(T) > 1 %will be true at index K if V(K) is not unique

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