point3d

I have a Point3d array, Z values are always zero. How can I have the maximum and minimum values of Y axis for every similar X values? Sample Point 3d Array: List[0] = (10,5,0) List[1] = (10,6,0) List[2] = (10,9,0) List[3] = (7,2,0) List[4] = (7,5,0) List[5] = (7,8,0) List[6] = (7,11,0)...