Sort the Harris corner coordinates and extract only the four corner coordinates

Hello,

I have an edge image where the corners are detected using Harris corner detection.The corners are plotted on the Edge image. I have extracted the corner coordinates and concatenated the x and y coordinates in a single array(Coordinates).I have sorted these coordinates. I am sending here the code snippet for sorting the x and y coordiantes

B=sortrows(Coordinates);
X=[true;diff(B(:,1))>0];
Sorted_Elements=B(X,:);

I get the sorted elements stored in Sorted_Elements array. Now i need to extract the four corner coordinates as follows:

TopLeft Coords=[Minx,miny]; RightTop Coords=[Maxx,Maxy]; LeftBottomCoords=[Maxx,Miny]; BottomRightCoords=[Maxx,Maxy]

I have attached the image .

 How can I find these coordinates. Please let me know the function in MATLAB to do this

Thanks Pankaja