How to return multiple values in loop?

Question

I'm just trying to return the multiple value in the loop. How this can be done, if I wish to return the last 20 value of x and y. here is the code:

contract Bar{

    struct Foo{
        uint x;
        uint y;
    }
    mapping(uint => Foo[]) foo;

    function add(uint id, uint x , uint y)  {
        foo[id].push(Foo(x, y));
    }

    function get(uint id, uint index) public returns(uint, uint){
      //  return foo[id][index].x;
      {
      var a = foo[id][index].x;
      var b = foo[id][index].y;
      }
      return (a,b);
    }

    function get_last_ten(uint id) constant returns(uint[20]){
    uint[20] memory lastItems;
    for(uint i=0;i<20;i++){
        if(foo[id].length>i){
            lastItems[i] = foo[id][foo[id].length-i-1].x;
        }
    }
    return lastItems;
}
}

Answer 1

You can either return 2 fixed-size arrays, like this:

function getLastTen(uint id) constant returns(uint[10], uint[10]){
    uint[10] memory lastX;
    uint[10] memory lastY;
    Foo[] storage arr = foo[id];
    uint len = arr.length;
    for(uint i=0;i<20;i++){
        if(len>i){            
            lastX[20 - 1 - i] = arr[len - 1 - i].x;
            lastY[20 - 1 - i] = arr[len - 1 - i].y;
        }
    }
    return (lastX, lastY);

or interleave them in one uint[20] with something like

            lastXY[20 - 1 - i * 2] = arr[len - 1 - i].x;
            lastXY[20 - 1 - i * 2 + 1] = arr[len - 1 - i].y;

20 - 1 instead of 19 is intentional.