Compare Two Lists Via One Property Using LINQ

Question

Say I have the following:

    class Widget1{         public int TypeID { get; set; }         public string Color { get; set; }     }      class Widget2     {         public int TypeID { get; set; }         public string Brand { get; set; }     }      private void test()     {         List<Widget1> widgets1 = new List<Widget1>();         List<Widget2> widgets2 = new List<Widget2>();         List<Widget1> widgets1_in_widgets2 = new List<Widget1>();          //some code here to populate widgets1 and widgets2          foreach (Widget1 w1 in widgets1)         {             foreach (Widget2 w2 in widgets2)             {                 if (w1.TypeID == w2.TypeID)                 {                     widgets1_in_widgets2.Add(w1);                 }             }         }     } 

I am using two foreach loops to compare the lists by TypeID to populate a third list. Is there any other way using LINQ to compare these two lists via the TypeID? Perhaps using Interstect or some other function?

Answer 1

You can do this

widgets2.Where(y=>widget1.Any(z=>z.TypeID==y.TypeID)); 

Answer 2

What you want here is a Join.

var widgets1_in_widgets2 = from first in widgest1     join second in widgets2     on first.TypeID equals second.TypeID     select first; 

Intersect can be more or less thought of as a special case of Join where the two sequences are of the same type, and can thus be applied for equality instead of needing a projection for each type to generate a key to compare. Given your case, Intersect isn't an option.

If a particular ID is duplicated in your second set and you don't want the item to be duplicated in the results then you can use a GroupJoin instead of a Join:

var widgets1_in_widgets2 = from first in widgest1     join second in widgets2     on first.TypeID equals second.TypeID     into matches     where matches.Any()     select first;