matrix 9x9 with duplicate values
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i have matrix C9x9 with duplicates. i must find duplicate above main diagonale. when i find first duplicate the searching stop and print this duplicate? thanks
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goran
il 19 Gen 2014
2 Commenti
Mischa Kim
il 19 Gen 2014
Hello goran, could you please post follow-up questions as comments, not as answers? To your question: the first duplicate above the diagonal (searching from left to right, top to bottom) is the 3 at position (1,2).
Più risposte (5)
Mischa Kim
il 19 Gen 2014
Modificato: Mischa Kim
il 19 Gen 2014
This should do. For a 3x3 matrix, as an example:
A = [1 3 2; 4 5 1; 3 1 1]
A_unique = unique(tril(A, -1));
FLAG = false;
for ii = 1:length(A(1,:))
for jj = ii+1:length(A(1,:))
if (length(A_unique) == length(unique([A_unique; A(ii,jj)])))
display(A(ii,jj))
FLAG = true;
break;
end
end
if FLAG
break;
end
end
7 Commenti
goran
il 19 Gen 2014
1 Commento
Mischa Kim
il 19 Gen 2014
Modificato: Mischa Kim
il 19 Gen 2014
Hello goran, the algorithm only searches above the diagonal. That's because of the indexing of the for loop ( jj = ii+1! ):
for ii = 1:length(A(1,:))
for jj = ii+1:length(A(1,:))
You can verify by simply printing the indices of the matrix elements.
goran
il 19 Gen 2014
1 Commento
Mischa Kim
il 19 Gen 2014
It is. See the display command. Simply run the code above, change the matrix and verify.
Andrei Bobrov
il 19 Gen 2014
Modificato: Andrei Bobrov
il 20 Gen 2014
function test1
A = randi(15,3)
B=A;
B(tril(B)>0)=nan;
C=B(~isnan(B));
[a,b] = unique(C,'first');
[~,ii] = sort(b);
c = histc(C,a);
out0 = [a(ii),c(ii)];
out = out0(find(out0(:,2)>1,1,'first'),1);
if isempty(out), disp('no duplicates'); end
end
4 Commenti
Harry Commin
il 9 Feb 2014
To extract only the upper triangular numbers into a column vector, you could use:
Aupper = A(triu(ones(size(A)))==1);
I think it is easier to find all duplicates than just the 'first' one. (How do we even define "first"?). However, assuming we want to progress through A column-wise, we could use:
B = unique(Aupper,'stable');
first_duplicate = Aupper(find(Aupper(1:length(B)) ~= B, 1))
The first line finds unique values in the order they appear. The second line finds the first place where the input vector and the 'uniques' are different (i.e. the first duplicate) and prints out that value.
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