c# - Group, Sort, and then Merge to a Observable Collection? -

i have list of items have "displayorder" property. can either have null or int value. if has int value, has priority , should in 1st group of observable collection. items in 1st group sorted displayorder.

if null, belongs 2nd group, sorted alphabetically.

the 1st group , 2nd group combined main items collection observable collection bind listview.

this current code though worried if there optimal way of doing it.

var mainitemcollection = new observablecollection<mainitemviewmodel>(); var itemswithproperty = new observablecollection<mainitemviewmodel>(); var itemswithnullproperty = new observablecollection<mainitemviewmodel>();  foreach (var item in dataobject.mainitems) {     if (item.displayorder == null)         itemswithnullproperty.add(new mainitemviewmodel(item));     else         itemswithproperty.add(new mainitemviewmodel(item)); }  itemswithproperty = new observablecollection<mainitemviewmodel>(itemswithproperty.orderby(c => c.displayorder)); itemswithnullproperty = new observablecollection<mainitemviewmodel>(itemswithnullproperty.orderby(c => c.title));  //add priorities first sorted displayorder 1,2,3,4 foreach (var c in itemswithproperty) {     mainitemcollection.add(c); }  //add without priority sorted alphabetically foreach (var c in itemswithnullproperty) {     mainitemcollection.add(c); } 

thank you!

get items displayorder=null & order them title:

itemswithnullproperty=dataobject.mainitems.where(x=>x.displayorder==null).orderby(o=>o.title).tolist(); 

get items displayorder(all items except above query) & order them displayorder:

itemswithproperty= dataobject.mainitems.except(itemswithnullproperty).orderby(o=>o.displayorder).tolist(); 

fill data in maincollection:

var allitems = mainitemcollection.concat(itemswithproperty)                                     .concat(itemswithnullproperty)                                     .tolist();