Intersect two object lists on a common property and then compare a different property

Question

I have two lists

List<objA> List1 List<objA> List2

I want to compare these two list on ID field, once a match is found I want to compare another field Distace amongst these two lists and grab the object with the lower value.

Using Linq isn't is not giving the result I want, atleast for the first part of the problem.

var test = List1.Select(x => x.ID) .Intersect(List2.Select(y => y.ID));

Answer 1

Here's one way you could do this with Linq. Firstly, join the two lists together with Union . Then, group them by the Id field. Lastly, order those sub lists by Distance within the grouping, and take the first one of each to get a list of objects by Id with the minimum available distance.

var aList = new[]
{
    new SomeObject() { Id = 1, Distance = 3 },
    new SomeObject() { Id = 2, Distance = 5 }
};

var bList = new[]
{
    new SomeObject() { Id = 1, Distance = 2 },
    new SomeObject() { Id = 2, Distance = 6 }
};

var results = aList
    .Union(bList)
    .GroupBy(a => a.Id, a => a)
    .Select(a => a.OrderBy(b => b.Distance).First());