conditionally removing rows dependent on values of other rows

I have a set of points in a matrix that will be plotted as points in a x,y such it ends up looking like:

A:

   2 0

   3 0

   4 0

   2 1

   3 1

   4 1

   ...

   2 8

   3 8

   4 8

   ...

(except with much more data)

giving a plot resembling:

 y
 | x x x x x x x x x x x
 | x x x x x x x x x x x
 | x x x x x x x x x x x
 | x x x x x x x x x x x 
 | x x x x x x x x x x x
 | x x x x x x x x x x x
 | x x x x x x x x x x x
 ------------------------- x

I am trying to set boundary conditions such that I eliminate all the values outside a-x < y < a+x, where a is a constant, so that I can end up with something like this:

 y
 |                 x x x
 |               x x x x
 |             x x x x 
 |           x x x x  
 |         x x x x 
 |       x x x x  
 |     x x x x  
 ------------------------- x

I would also like to restrict the values that x can be in order to isolate a specific region of points, then count how many I have left while being able to see it visually on a plot.

I have tried writing a few conditions, such as A(A(:,1)>A(:,2))=[], and even putting it in a loop, but it doesn't seem to work how I would like it to.

Any suggestions would be appreciated. I am still very green in terms of programming.

Answer 1

[Mohammad Abouali]

[x,y]=ndgrid(1:10);
A=[x(:) y(:)];

a=3;

mask = ((x-a)<y) & (y<(a+x));
plot(A(mask,1),A(mask,2),'x','MarkerSize',15,'LineWidth',2)

[K]

Thank you! This worked very well.

[Mohammad Abouali]

You are welcome. If this concludes your question, would you please mark the answer as "accepted".