How to use an index of a vector as a value in another matrix?

Hi, I have a vector x=[1 1 2 2 3] and a matrix [1 3 ; 1 4 ; 2 3 ; 2 4]

The logic that I want to create says that the index of the latter of the similar values is extracted. Then, wherever the matrix has that value, that row becomes zero. For example, the indices of first two similar values in vector x are 1 and 2. I want those rows in the matrix that contains the value 2, should become zero. Same is the case for 3 and 4.

In the end, the matrix should only contain a single row i.e. [1 3]

[the cyclist]

The question is very unclear to me. I have no idea what you want.

[Matthew Eicholtz]

I think when you say "becomes zero", you mean "is removed", correct?

[Syed Fahad Hassan]

Yes Matthew, I want the row to be removed

Answer 1

[dpb]

>> x=[1 1 2 2 3] ;
>> m= [1 3 ; 1 4 ; 2 3 ; 2 4];
>> m(any(ismember(m,find(diff(x))),2),:)=[]
m =
   1     3
>>

[Stephen23]

+1 nice use of indexing.

Answer 2

[Alex Kerzner]

I'm sure someone can come up with something more clever and efficient, but here's something hack-y that might give you some ideas for improvements. Assuming the matrix is called M :

    repeats = [];
        while ~isempty(x)
            if numel(find(x == x(1))) >= 2 %If we have multiple of them
                repeats(end+1) = max(find(x==x(1))); %add the largest index to the list
                x(find(x==x(n))) = []; %remove all the duplicates
            else
                x(1) = []; %If no duplicates, just get rid of it
            end
        end
    for r = repeats
        [i,~] = find(M == r);
        M(i,:) = [];
    end

[Syed Fahad Hassan]

what is 'n' in your logic?

Answer 3

[Matthew Eicholtz]

How about this?

Assume you have the inputs:

x = [1,1,2,2,3];
y = [1,3; 1,4; 2,3; 2,4];

Then, you can find indices to remove by:

[~,ind,~] = unique(fliplr(x));
ind = length(x)-ind+1;

Then, remove the rows containing any of those indices:

y(any(ismember(y,ind),2),:) = [];

[Matthew Eicholtz]

Note, my approach will remove indices of values that exist only once in x (e.g., the 3). It is unclear from the question whether this should be allowed or not.