matrix 9x9 with duplicate values

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goran 2014-1-19

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回答： Harry Commin 2014-2-9

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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Answer 1

goran 2014-1-19

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i changed matrix to 4x4 and i sould received like solution duplicate above main diagonal nuber 4, i receive solution 3. why?

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Mischa Kim 2014-1-19

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).

goran 2014-1-19

sorry. code is ok. can you explain your code? what is FLAG?

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Answer 2

Mischa Kim 2014-1-19

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编辑：Mischa Kim 2014-1-19

在 MATLAB Online 中打开

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

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goran 2014-1-19

when my matrix has elements like on pictures then no duplicates why?

i think that duplicate is 1.1

goran 2014-1-23

在 MATLAB Online 中打开

my solution for this problem is

if true
  A=[1 3 2.2 130 5.4 60 8.9 8 45;2 58 4 8 6.5 69 78 23 1.1;7 8 4 69 65.3 6.7 89.3 102.3 45;3 4 3 1 8.9 1.1 59 4.5 65;
 1 23 2.5 45 5.6 7.9 8.78 65 89; 12 897 67 0.5 102.3 7.8 9 11 567; 494 123 256 28.6 2.2 123 891 111 11.1;
 45 12 1.2 2.6 58.4 36 45.7 12.1 78.6; 1.1 2.3 4.5 36 25 11.6 89.3 1.1 1]
%A=rand(9,9)
  Agd=(triu(A, 1)); %selektuje elemente iznad glavne diagonale
Agdv=Agd(:); %kreira vektor
Agdv(Agdv==0)= []; %brise nule iz vektora
Aj=unique(Agd); %selektuje jedinstvene vrednosti iz Agd
Aj(Aj==0)=[];  %brise nule iz jedinstvenih vrednosti
if (length(Aj)~=length(Agdv)) %proverava da li broj jedinstvenih vrednosti razlicit u odnosu na Agdv, ako jesu onda postoje duplikati, ako ne stampa nema istih elemenata
  [~,~, IAgdv] = unique(Agdv, 'stable'); %odredjuju se indeksi jedinstvenih vrednosti u nepromenjenom redosledu u Agdv
  idx = find(diff(IAgdv)-1, 1)+1; %nalazi indeks koji se dva puta ponavlja
  el=Agdv(idx); %dodeljuje vrednost tog indeksa promenljivoj el
  fprintf('Prvi isti element koji se pojavio je: %.4f \n',el) % stampa vednost promenljive el
else
  disp('Nema istih elemenata')
end
end

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Answer 3

goran 2014-1-19

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the searching need to work just on elements above main diagonal. your code search entire matrix

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Mischa Kim 2014-1-19

编辑：Mischa Kim 2014-1-19

在 MATLAB Online 中打开

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.

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Answer 4

goran 2014-1-19

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also, i need that duplicate values is printed, not how much duplicate values have?

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Mischa Kim 2014-1-19

It is. See the display command. Simply run the code above, change the matrix and verify.

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Answer 5

Andrei Bobrov 2014-1-19

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编辑：Andrei Bobrov 2014-1-20

在 MATLAB Online 中打开

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

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Andrei Bobrov 2014-1-20

编辑：Andrei Bobrov 2014-1-20

use file test1.m:

goran 2014-1-20

thank's sorry can you explain your code?

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Answer 6

Harry Commin 2014-2-9

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在 MATLAB Online 中打开

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.