如何从矩阵中获取选择性行并以八度为单位形成新矩阵？

Question

Suppose I have a matrix in octave

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

Now I want to get only those rows where the last column is say equal to 5. I was wondering if there is a built in function for this, cause right now am doing it like this.

collection = [];
for i = 1 : size(matrix,1),
    if(matrix(i,3) == 5),
        collection = [collection; matrix(i,:)];
    end
end

I would be fine if there is such a method for single column matrices.

Answer 1

You can do it using logical indexing on the last column so for example

A(:,end) == 5

returns a logical matrix which is true for the rows you want and false otherwise. We can use this to select rows like so

ind = A(:,end) == 5;
A(ind,:); 

you can even just do it inline:

A(A(:,end)==5,:)