How Detect duplicate value in each column and replace first value with zero?

For example

A = [ 5  3  2 5 1 3  1 1 2 2;
      5  8  6 6 1 4  4 2 3 3;
      7  9  9 7 4 8 10 6 4 7;
      8 10 10 9 9 8 10 6 5 7];

In first column 5 duplicate and in five column 1 duplicate I want replace first duplicated values with 0

[Image Analyst]

Running your code I get:

A =
     5     3     2     5     1     3     1     1     2     2
     5     8     6     6     1     4     4     2     3     3
     7     9     9     7     4     8    10     6     4     7
     8    10    10     9     9     8    10     6     5     7

I do NOT see 5 duplicates in column 1. I don't even see 5 values of anything in column 1 which has only 4 elements. In column 5 I do seem 1 duplicate since the 1 of row 1 is duplicated in row 2. But you need to say whether a number is a duplicate if it's adjacent to the same number, or can it appear apart/separate from it. For example, is the third 10 in row 4 a duplicate or not.

But the main problem is you saying there are 5 duplicates in column 1. Explain that.

[the cyclist]

I think they mean that the number 5 is duplicated in the first column, and that the number 1 is duplicated in the fifth column. (Similarly the number 8 is duplicated in the sixth column, and so on.)

[Stephen23]

See duplicate:

https://www.mathworks.com/matlabcentral/answers/332919-how-detect-duplicate-value-in-each-column-and-replace-one-value-with-zero

Answer 1

[the cyclist]

If your values are always sorted, as in your example, then I believe this will compactly do what you want:

indexToDuplicates = [nan(1,size(A,2));diff(A)]==0;
A(indexToDuplicates) = 0;

You don't even have to split that into two lines, but I thought it might be clearer what I am doing. You could do

A([nan(1,size(A,2));diff(A)]==0) = 0;