set unique values in matrix for each column new to 0

Question

Frederik Reese 2022-7-13

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https://ww2.mathworks.cn/matlabcentral/answers/1758725-set-unique-values-in-matrix-for-each-column-new-to-0

编辑： Bruno Luong 2022-7-13

采纳的回答： Ruchika P Barman

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Hi,

I want to set the dublicate values to zero:

The problem with this code is that it sets all duplicate values to 0, even across columns. I want the duplicate values to be removed only per column E.g. the error in my code:

0 0 0

0 0 1

1 0 2

2 1 3

2 2 4

is going to

0 0 0

1 0 0

2 0 3

0 0 4

0 0 0

I want

0 0 0

0 0 1

1 0 2

2 1 3

0 2 4

0 0 0

DOK_HQ10000_FD_zeitlich_neu= zeros(size(DOK_HQ10000_FD_zeitlich))
[~,pos] = unique(DOK_HQ10000_FD_zeitlich,'first')
DOK_HQ10000_FD_zeitlich_neu(pos)=DOK_HQ10000_FD_zeitlich(pos)

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Answer 1

Ruchika P Barman 2022-7-13

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It is my understanding that you are trying to set the duplicate values to zero considering the elements columnwise in the matrix.

M = [0 0 0 ; 0 0 1; 1 0 2 ; 2 1 3 ; 2 2 4 ; 2 2 4]
M = 6×3
     0     0     0
     0     0     1
     1     0     2
     2     1     3
     2     2     4
     2     2     4
ans1=[];
[~,col]=size(M);
for c=1:col
    x=(M(:,c))';
    y = [x(1) diff(x)];
    y = find(y==0);
    z = x;
    z(y)=0;
    ans1 = [ans1;z];
end
ans1=ans1'
ans1 = 6×3
     0     0     0
     0     0     1
     1     0     2
     2     1     3
     0     2     4
     0     0     0

This should solve your problem, thank you.

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Frederik Reese 2022-7-13

Thanks for your help

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Answer 2

Bruno Luong 2022-7-13

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It looks like your repeated elemenst are adjacent

M = [0 0 0 ; 0 0 1; 1 0 2 ; 2 1 3 ; 2 2 4 ; 2 2 4]
M = 6×3
   0     0
   0     1
   0     2
   1     3
   2     4
   2     4
M.*(diff([nan(size(M(1,:))); M],1,1)~=0)
ans = 6×3
   0     0
   0     1
   0     2
   1     3
   2     4
   0     0

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Answer 3

Bruno Luong 2022-7-13

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This works for repeated elements that are in any order in the columns

M = randi(4,10,3)
M = 10×3
     3     1     3
     1     2     4
     2     3     3
     3     2     4
     3     3     4
     4     3     1
     4     1     2
     2     2     4
     4     4     2
     2     3     1
[m,n]=size(M);
IJ = cell(n,1);
v = cell(n,1);
for j=1:n
    [v{j},IJ{j}] = unique(M(:,j),'stable'); 
    IJ{j}(:,2)=j; 
end
accumarray(cat(1,IJ{:}), cat(1,v{:}), [m,n])
ans = 10×3
     3     1     3
     1     2     4
     2     3     0
     0     0     0
     0     0     0
     4     0     1
     0     0     2
     0     0     0
     0     4     0
     0     0     0

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Answer 4

Bruno Luong 2022-7-13

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https://ww2.mathworks.cn/matlabcentral/answers/1758725-set-unique-values-in-matrix-for-each-column-new-to-0#answer_1006805

编辑：Bruno Luong 2022-7-13

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Another solution without assum^tion of M is sorted by column

M = randi(4,10,3)
M = 10×3
   4     2
   2     2
   2     3
   4     3
   2     2
   3     1
   4     3
   2     4
   2     1
   2     1
[m,n]=size(M);
[S,i] = sort(M);
M(i+(0:n-1)*m) = S.*~~[true(1,n);diff(S)]
M = 10×3
   4     2
   2     0
   0     3
   0     0
   0     0
   3     1
   0     0
   0     4
   0     0
   0     0