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

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Syed Fahad Hassan on 3 Aug 2017
Closed: MATLAB Answer Bot on 20 Aug 2021
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]
Syed Fahad Hassan on 4 Aug 2017
Yes Matthew, I want the row to be removed

dpb on 3 Aug 2017
>> 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 on 4 Aug 2017
+1 nice use of indexing.

Alex Kerzner on 3 Aug 2017
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 on 4 Aug 2017
what is 'n' in your logic?

Matthew Eicholtz on 3 Aug 2017
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),:) = [];