In a sorted vector ,how do I compare first element to other elements and then find if there are any duplicates , if yes take their indexes and replace it with 0

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Sagar Saxena 2018-11-5

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评论： Sagar Saxena 2018-11-15

A = [ 1, 1 , 2, 3, 4]

I want to first compare first element to all other elements, if there is any duplicate (like 1, 1 in this example) I need to replace it with 0.

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Stephen23 2018-11-6

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编辑：Stephen23 2018-11-6

在 MATLAB Online 中打开

For a sorted row vector. Find duplicates of the first element, as you requested:

>> A = [1,1,2,3,4];
>> X = A(1)==A;
>> X(1) = false;
>> A(X) = 0
A =
   1   0   2   3   4

Or perhaps you meant to find all duplicates, not just of the first element:

>> A = [1,1,2,3,4];
>> X = [false,diff(A)==0];
>> A(X) = 0
A =
   1   0   2   3   4

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Stephen23 2018-11-15

编辑：Stephen23 2018-11-15

在 MATLAB Online 中打开

PS: taking a wild guess here, that you want to perform this for each page (i.e. along the third dimension) independently:

>> C = {[9,3,7;6,3,8;3,7,9],[8,4,8;2,6,7;2,9,5]};
>> A = cat(3,C{:})
A(:,:,1) =
   9   3   7
   6   3   8
   3   7   9
A(:,:,2) =
   8   4   8
   2   6   7
   2   9   5
>> DM = sort(sort(A,1),2)
DM(:,:,1) =
   3   3   7
   3   6   8
   7   9   9
DM(:,:,2) =
   2   4   5
   2   6   7
   8   8   9
>> X = DM(1,1,:)==DM;
>> [~,~,P] = ind2sub(size(X),find(X));
>> V = accumarray(P,1,[],@(v)1/sum(v));
>> A(X) = V(P);
>> A(~X) = 0
A(:,:,1) =
   0.33333   0.33333   0.00000
   0.33333   0.00000   0.00000
   0.00000   0.00000   0.00000
A(:,:,2) =
   0.50000   0.00000   0.00000
   0.50000   0.00000   0.00000
   0.00000   0.00000   0.00000
   

If that is not the output that you expect then please show me what output you need to get.

Sagar Saxena 2018-11-15

Thanks Stephen, This works perfectly fine for what I need and you are right instead of using dimension I should be using the term page. Let me try puting this peice of logic into my actual code. Will let you know if I am stuck any further.

But this really helped, Thanks a lot!

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TADA 2018-11-5

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编辑：TADA 2018-11-5

how about unique(A)?

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madhan ravi 2018-11-6

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编辑：madhan ravi 2018-11-6

在 MATLAB Online 中打开

A = [ 1, 1, 2, 3, 4];
[~,c,~]=(unique(A,'first'));
idx=(ismember((1:numel(A)),c));
A(~idx)=0

c is the index of unique values in A the left out indices contain duplicate values. The above method works for arbitrary vectors too not only for sorted vector.