add generic list item to another existing list item using c# -

i have generic list filled items. in list have 1 column unique (like id). , have generic list other items , same id column. way fill items lists:

foreach (string s in l1) {     gridviewsource src = new gridviewsource();     src.test = "id" + s;      list.add(src); }  foreach (string s in l2) {     gridviewsource src = new gridviewsource();     src.test = "id" + s;     src.test2 = "somerandomtext" + s;      list2.add(src); } 

what i'm trying add items list2 list if have same id. should add item list2 id "id3" item "id3" of list. merging. don't want add them bottom of list or insert them between items. tried concat method it's adding items add end of list:

list = list.concat(list2).tolist(); 

edit:

i try explain way:

my list looks this:

[0] => test = "id1", test2 = "" [1] => test = "id2", test2 = "" [2] => test = "id3", test2 = "" [3] => test = "id4", test2 = "" [4] => test = "id5", test2 = "" 

and list2 looks this:

[0] => test = "id1", test2 = "somerandomtext1" [1] => test = "id2", test2 = "somerandomtext2" [2] => test = "id3", test2 = "somerandomtext3" 

and when merge lists, should this:

[0] => test = "id1", test2 = "somerandomtext1" [1] => test = "id2", test2 = "somerandomtext2" [2] => test = "id3", test2 = "somerandomtext3" [3] => test = "id4", test2 = "" [4] => test = "id5", test2 = "" 

but looks this:

[0] => test = "id1", test2 = "" [1] => test = "id2", test2 = "" [2] => test = "id3", test2 = "" [3] => test = "id4", test2 = "" [4] => test = "id5", test2 = "" [5] => test = "id1", test2 = "somerandomtext1" [6] => test = "id2", test2 = "somerandomtext2" [7] => test = "id3", test2 = "somerandomtext3" 

any suggestions?

so need merge on item level, not on list level.

i'm sure there clever way using linq, don't have experience linq, can suggest simple nested loops:

foreach (gridviewsource src1 in list1) {     foreach(gridviewsource src2 in list2)     {         if(src1.test1 == src2.test1)         {             src1.test2 = src2.test2;         }     } }