Question

I want to sort a List of coordinates first by its x coordinates and and then by its y coordinates:

Orginal: (7,8)(10,22)(7,3)(5,10)(20,14)(7,10)(7,3)

First Step by x: (5,10)(7,8)(7,3)(7,10)(7,3)(10,22)(20,14)

Second Step by y: (5,10)(7,3)(7,3)(7,8)(7,10)(10,22)(20,14)

I have already a functions that works for the first step:

function SortCoords(Item1: Pointer; Item2: Pointer): Integer;
var
line1 : Coords;
line2 : Coords;
begin
  line1 :=  Coords;(Item1);
  line2 :=  Coords;(Item2);

  if (line1.X < line2.X) then 
    result := -1
  else if (line1.X > line2.X) then 
     result := 1
  else
     result := 0;

end; 

But i dont get the second step.

Answer 1

If you want items sorted by a secondary key, this is only going to be important when the first keys are equal. In your example, this is the result := 0; case.

So something like this:

if (line1.X < line2.X) then 
    result := -1
  else if (line1.X > line2.X) then 
     result := 1
  else if (line1.Y < line2.Y) then 
    result := -1
  else if (line1.Y > line2.Y) then 
     result := 1
  else
     result := 0;

Might do what you want.