Delete the row of matrix

I want to delete multiple rows of matrix.

For example,

Matrix A contains X in the first column, and Y in the second column. Note that X and Y does not have to be a whole number .

A = [ 1.122 2.111; 1.122 2.3, etc,....]

If X values are in the interval of [1.12 -1.125] and Y values are in the interval of [2.12-2.3], then delete this row.If X is in the range but Y is not, then dont delete them. Note that I have to search the matrix A to find whether X and Y in the interval that I defined, and then delete them. From the example above, the second row needs to delete by looking at it. But I need to search them for the huge matrix which I cant use eye to find them. I need you guys helps.

Thanks.

[Hikaru]

Is this homework?

If it is, I'll give you a hint on where to start. Say you have a vector b and the condition c to determine which element will be deleted.

b = [1 2 3 0];
c = b>=3;
b(c)=[] % this will delete that element

[Laura]

This is not a homework. Thanks though.

Answer 1

[Guillaume]

It's fairly basic matlab matrix manipulation. Use logical indexing:

A(A(:, 1) >= 1.12 & A(:, 1) <= -1.125 & A(:, 2) >= 2.12 & A(:, 2) <= -2.3, :) = []

% A(:, 1) is your X, A(:, 2) is your Y
% A(:, 1) >= 1.12 & A(:, 1) <= -1.125 is all the rows of A for X in [1.12 -1.125] (1)
% A(:, 2) >= 2.12 & A(:, 2) <= -2.3   is all the rows of A for Y in [2.12 -2.3]   (2)
% (1) & (2) is X in [1.12 -1.125] AND Y in [2.12 -2.3]                            
% A(condition, :) = []  remove all the rows of A that fulfill the condition

[Laura]

Thanks so much Guillaume. It works fine. However, I want to ask why it does not work if I try this:

 rx=find(A(:, 1) >= 1.12 & A(:, 1) <= -1.125);

 ry=find(A(:, 2) >= 2.12 & A(:, 2) <= -2.3);

 A(rx,ry)=[];

it gave me an error as "Subscripted assignment dimension mismatch".

Thanks again.

[Guillaume]

You seem to be a bit confused about array indexing. In

A(rx, ry)

ry is the columns of A. You've only got two columns.

If you wanted to use your method, you'd have to do:

rx=find(A(:, 1) >= 1.12 & A(:, 1) <= -1.125);
ry=find(A(:, 2) >= 2.12 & A(:, 2) <= -2.3);
A(intersect(rx, ry), :) = [];

It's a lot more work though than:

logicalx = A(:, 1) >= 1.12 & A(:, 1) <= -1.125;
logicaly = A(:, 2) >= 2.12 & A(:, 2) <= -2.3;
A(logicalx & logicaly, :) = [];