Given an IList<Foo> with a data set that looks like this: ID CHILD PARENT TYPE 1 102 101 UPSELL 1 103 101 UPSELL 2 102 101 BONUS 2 104 103 BONUS 3 102 101 BONUS 4 102 101 PRODUCT 4 104 102 PRODUCT How can I use LINQ to find the intersection of Parent and Child values withing each ID? Desired output is ID CHILD PARENT TYPE 4 102 101 PRODUCT