0 10 15 
0 21 26 
0 27 31 
1  3 15 
1 10 13 
1 15 21 
2 38 55 
3  8 21 
3 22 41 
 

0 10 31 
1  3 21 
2 38 55 
3  8 41 

var _array = [ 
[0,10,15], 
[0,21,26], 
[0,27,31], 
[1,3,15], 
[1,10,13], 
[1,15,21], 
[2,38,55], 
[3,8,21], 
[3,22,41], 
] 
 
if(_array.length>1){ 
    _finalArray = [[_array[0][0], _array[0][1]]]; 
    for(var a = 1; a<_array.length; a++){ 
        if(_array[a-1][0] != _array[a][0]){ 
            _finalArray.push(_array[a-1][2]);// letzte y2-Koordinate aus vorhergehendem block 
            _finalArray.push(_array[a][0]); 
            _finalArray.push(_array[a][1]); 
            } 
        if(a==_array.length-1) _finalArray.push(_array[a][2]); 
        } 
    } 
 
$.writeln (_finalArray) 

    /*array*/Array.prototype.sortThis=function(/*String*/field, reverse) 
    { 
        if (reverse == null) var reverse = false; 
        if (reverse) return this.sort(sortthisDown); 
        else  return this.sort(sortthisUp); 
          
        /*int*/function sortthisUp(e1, e2) 
        { 
            if (field==null) 
            { 
                if (e1<e2) return -1; 
                if (e1>e2) return 1; 
                return 0; 
            } 
            else  
            { 
                if (e1[field]<e2[field]) return -1; 
                if (e1[field]>e2[field]) return 1; 
                return 0; 
            } 
        } 
        /*int*/function sortthisDown(e1, e2) 
        { 
            if (field==null) 
            { 
                if (e1>e2) return -1; 
                if (e1<e2) return 1; 
                return 0; 
            } 
            else  
            { 
                if (e1[field]>e2[field]) return -1; 
                if (e1[field]<e2[field]) return 1; 
                return 0; 
            } 
        } 
    } 
main(); 
 
function main() 
{ 
    /*Array*/var toExtract = [[0,21,26],[0,27,31],[1,3,15],[1,10,13],[2,38,55],[3,8,21],[3,22,41],[0,10,15],[1,15,21]]; 
    // sort pages 
    toExtract.sortThis(0); 
    /*Array*/var result = new Array(); 
    var i = 0; 
    if (toExtract.length == 0) return; 
    /*object*/var page = new Page(toExtract[i][0], [toExtract[i][1]], [toExtract[i][2]]); 
    for(i=1; i<toExtract.length; i++) 
    { 
        if (toExtract[i-1][0]== toExtract[i][0]) 
        { 
            page.y1.push(toExtract[i][1]); 
            page.y2.push(toExtract[i][2]); 
        } 
        else 
        { 
            result.push(page); 
            page = new Page(toExtract[i][0], [toExtract[i][1]], [toExtract[i][2]]); 
        }             
    } 
    result.push(page); 
    // now handle pages: 
    for (i=0; i<result.length; i++) 
    { 
        // sort y1, y2 in page: 
        result[i].y1.sortThis(); 
        result[i].y2.sortThis(); 
        // store result and delete not  needed elements 
        result[i].y1.length =1; 
        result[i].y2[0] = result[i].y2[result[i].y2.length-1]; 
        result[i].y2.length = 1; 
    } 
    // format for alert 
    /*string*/var o = ""; 
    for (i=0; i<result.length;i++) 
    { 
        o+= "Seite: " + result[i].number + " y1: " + result[i].y1 + " y2: " + result[i].y2 + "\n"; 
    } 
    alert(o); 
    return; 
    function Page(/*int*/number, /*float*/y1, /*float*/y2) 
    { 
        this.number = number; 
        this.y1 = y1; 
        this.y2 = y2; 
    } 
}