Java: sort a list of lists -
i have list of lists of points ie: list<list<point>>. e.g.:
list<point> lp; list<list<point>> llp; llp.add(lp); lpwould first line of matrix (x=0). llpis whole matrix.
i want list ascendingly sorted according both x , y of each point. managed internal list sorted not whole list. can me please? thank you. here code sort internal list (ie. first line of matrix) according y.
private void ord_horiz (list<point> tab) { boolean ordered_horiz = false; int size = tab.size(); while(!ordered_horiz) { ordered_horiz = true; for(int i=0 ; < size-1 ; i++) { if(tab.get(i).y > tab.get(i+1).y) { swap(tab, i, i+1); ordered_horiz = false; } } size--; } } private void swap(list<point> tab, int ind1, int ind2) { point c; c = tab.get(ind1); tab.set(ind1, tab.get(ind2)); tab.set(ind2, c); } here code wrote far:
collections.sort(tab,new comparator<list<point>>(){ @override public int compare(list<point> o1, list<point> o2) { if(o1 != null && o2 !=null) { point var1 = o1.get(0); int var1_x = var1.x; int var1_y = var1.y; point var2 = o2.get(0); int var2_x = var2.x; int var2_y = var2.y; integer.compare(var1_x, var2_x); integer.compare(var1_y, var2_y); return /* shall return ? */; } return 0; } }); here screenshot of console output. want point sorted. http://imageshack.us/scaled/large/515/38zy.png
"i want sort external list according x , y, given x order of lp within llp , y order of elements of each lp in llp."
you should use custom comparator. assume each list within llp has same number of elements, , each list distinct x, following should work:
example
//create data list<list<point>> llp = new arraylist<list<point>>(); for(int i=0; i< 50; i++) { list<point> lp = new arraylist<point>(); for(int j=0; j<50; j++) lp.add(new point((int)(math.random()*1000), i)); llp.add(lp); } // comparators comparator<list<point>> comparator_rows = new comparator<list<point>>() { @override public int compare(list<point> o1, list<point> o2) { int = o2.get(0).y; int j = o1.get(0).y; if (i < j) { return 1; } else if (i > j) { return -1; } else { return 0; } } }; comparator<point> comparator_columns = new comparator<point>() { @override public int compare(point o1, point o2) { int = o2.x; int j = o1.x; if (i < j) { return 1; } else if (i > j) { return -1; } else { return 0; } } }; // sort rows collections.sort(llp, comparator_rows); // sort columns (list<point> element : llp) collections.sort(element, comparator_columns); //print elements int rowindex = 0, columnindex=0; (list<point> row : llp) { (point element : row) system.out.print("("+element.x+ "," + element.y +")|"); system.out.println(); } the above code gets first element of each row, , extracts x coordinate. x coordinate used sort rows.
update
if data mixed up, can use following code uses treemaps put elements supposed be. result jagged array.
//create data list<list<point>> llp = new arraylist<list<point>>(); for(int i=0; i< 50; i++) { list<point> lp = new arraylist<point>(); for(int j=0; j<50; j++) lp.add(new point((int)(math.random()*1000), (int)(math.random()*1000))); llp.add(lp); } //if data mixed need filter new rows based on x using treemap treemap<integer, treemap<integer,point>> data = new treemap<integer,treemap<integer,point>>(); (list<point> row : llp) { (point element : row) { treemap<integer,point> rowforx; if(data.containskey(element.x)) rowforx = data.get(element.x); else data.put(element.x, rowforx = new treemap<integer,point>()); //create specific row in treemap rowforx.put(element.y,element); } } //convert sorted treemap(s) lists llp.clear(); iterator<entry<integer, treemap<integer, point>>> = data.entryset().iterator(); while(it.hasnext()) llp.add(new arraylist<point>(it.next().getvalue().values())); //print elements int rowindex = 0, columnindex=0; (list<point> row : llp) { (point element : row) system.out.print("("+element.x+ "," + element.y +")|"); system.out.println(); }
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