Merge lists and pick properties from both

Question

I have two lists. List<A>, where the type A has two properties { x, y } and List<B> where the type B has two properties { y, z }.

I want to join the two lists on y and then pick x and z in my new list.

Is this possible using some a LINQ one-liner?

There are some fundamental questions that need answered before this can be solved. For example, what if multiple items exist for a particular value of `y`? And: What if only one of the two lists contains an entry for a particular value of `y`? What value would be used for the missing `x` or `z` data? — Matthew Watson, Feb 01 '21 at 12:59

SomeBody · Accepted Answer · 2021-02-01T13:16:36.580

4

I assume you have two types:

class A
{
   public int x {get; set;}
   public int y {get; set;}
}
    
class B
{
   public int y {get;set;}
   public int z {get;set;}
}

And your two lists:

List<A> a = new List<A> { new A { x = 1, y = 2 }, new A { x= 2, y = 3}};
List<B> b = new List<B> { new B { y = 2, z = 2 }, new B { y= 3, z = 3}};

You can join them with LINQ:

var joined = a.Join(b, a => a.y, b => b.y, (a,b) => new {a.x, b.z}).ToList();

You will have a List with two items: x=1, z=2 and x=2, z=3.

edited Feb 01 '21 at 13:16

answered Feb 01 '21 at 12:55

SomeBody

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1

Great! This was exactly what i was looking for :) – Daniel Gustafsson Feb 01 '21 at 13:00

Athanasios Kataras · Answer 2 · 2021-02-01T12:52:14.120

1

You are looking for linq Union

int[] ints1 = { 5, 3, 9, 7, 5, 9, 3, 7 };
int[] ints2 = { 8, 3, 6, 4, 4, 9, 1, 0 };

IEnumerable<int> union = ints1.Union(ints2);

foreach (int num in union)
{
    Console.Write("{0} ", num);
}

/*
 This code produces the following output:

 5 3 9 7 8 6 4 1 0
*/

Your case dotnetfiddle:

string[] ints1 = { "x", "y" };
string[] ints2 = { "y", "Z" };

IEnumerable<string> union = ints1.Union(ints2);

foreach (string num in union)
{
    Console.Write("{0} ", num);
}

edited Feb 01 '21 at 12:52

answered Feb 01 '21 at 12:48

Athanasios Kataras

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Very good example. It shows that a `Union` is a `Concat().Distinct()` – xanatos Feb 01 '21 at 12:51
Ok I realize I wasn't clear enough. So what I have is two list were the properties is X and Y or Y and Z. So the value of them is different and there is loads of values in each list. So I need to join the values of the properties Y – Daniel Gustafsson Feb 01 '21 at 12:53
1

I still don't understand the case. Can you please provide the example in your question? Objects have properties, lists have items. – Athanasios Kataras Feb 01 '21 at 12:55
OP is asking for a **single** list containing instances of **different** types. – MakePeaceGreatAgain Feb 01 '21 at 13:01
Ok, it didn't look like that at all to me. I got it from the accepted answer. – Athanasios Kataras Feb 01 '21 at 13:01

Merge lists and pick properties from both

2 Answers2