Combining two Lists of an Object into one

Question

I am currently developing an application that requires this senario.

Assuming I have this object

public class ObjectItem
{
   public int Id {get;set;}
   public int Name {get;set;}
   public int Sex {get;set;}
   public int Age {get;set;}
   public string Complexion {get;set;}
}

If we now have two lists of this object

var studentWithAge = new List<ObjectItem>
                  {
                    new ObjectItem {Id = 1, Name = "John", Age = 2},
                    new ObjectItem {Id = 2, Name = "Smith", Age = 5},
                    new ObjectItem {Id = 3, Name = "Juliet", Age = 7},
                  };

var studentWithSexAndComplexion = new List<ObjectItem>
                       {
                          new ObjectItem {Id = 1, Name = "John", Sex = "Male", Complexion = "fair"},
                          new ObjectItem {Id = 2, Name = "Smith", Sex = "Male", Complexion = " "},
                          new ObjectItem {Id = 3, Name = "Juliet", Sex = "Female", Complexion = "Blonde"},
                          new ObjectItem {Id = 4, Name = "Shittu", Sex = "Male", Complexion = "fair"},
                       };

I want to merge these two lists into just one. The end result should look like this.

var CompleteStudentData=new List<ObjectItem>
{
   new ObjectItem{Id=1,Name="John",Sex="Male", Complexion="fair",Age=2},
   new ObjectItem{Id=2,Name="Smith",Sex="Male", Complexion=" ", Age=5},
   new ObjectItem{Id=3,Name="Juliet",Sex="Female", Complexion="Blonde", Age=7},
   new ObjectItem{Id=4,Name="Shittu",Sex="Male", Complexion="fair", Age=0},
}

How do i achieve this? Using Union to merge the two list does not produce the desired result. I would appreciate your help.

AddRange()

Crowcoder
– Crowcoder

2015-02-28 16:23:41 +00:00
Commented Feb 28, 2015 at 16:23 — Crowcoder
– Crowcoder, Commented Feb 28, 2015 at 16:23
This looks like an outer join.

Tarik
– Tarik

2015-02-28 16:25:37 +00:00
Commented Feb 28, 2015 at 16:25 — Tarik
– Tarik, Commented Feb 28, 2015 at 16:25

aush · Accepted Answer · 2015-02-28 16:56:01Z

4

var result = StudentWithAge.Join(StudentWithSexAndComplexion, 
                                 sa => sa.Id,
                                 ssc => ssc.Id,
                                 (sa, ssc) => new ObjectItem
                                 {
                                    Id = sa.Id,
                                    Name = sa.Name, 
                                    Age = sa.Age, 
                                    Sex = ssc.Sex, 
                                    Complexion = ssc.Complexion
                                 }).ToList();

Or, avoiding creation of new objects:

var result = StudentWithAge.Join(StudentWithSexAndComplexion, 
                                 sa => sa.Id,
                                 ssc => ssc.Id,
                                 (sa, ssc) => 
                                 { 
                                    sa.Sex = ssc.Sex; 
                                    sa.Complexion = ssc.Complexion; 
                                    return sa;
                                 }).ToList();

And if you want to add students presented only in the second list, than also:

result.AddRange(StudentWithSexAndComplexion.Where(ssc => !StudentWithAge.Any(sa => sa.Id == ssc.Id)));

edited Feb 28, 2015 at 16:56

answered Feb 28, 2015 at 16:29

aush

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1 Comment

Rubidium 37 Over a year ago

Due to the nature of the ObjectItem and the contents of the two lists, could be better to join by Name and not Id.

Community · Accepted Answer · 2017-05-23 12:06:25Z

1

Since it's possible that your collections will not have a 1-to-1 correspondence, you would have to do a full outer join. See here for how you can compose it that way.

Here's one way you can get similar results.

Collect all the keys (the ids) from both collections, then perform a left join with each of the collections, then combine the results.

var ids = studentWithAge.Select(s => s.Id)
    .Union(studentWithSexAndComplexion.Select(s => s.Id));
var query =
    from id in ids
    from sa in studentWithAge
                    .Where(sa => sa.Id == id)
                    .DefaultIfEmpty(new ObjectItem { Id = id })
    from ssc in studentWithSexAndComplexion
                    .Where(ssc => ssc.Id == id)
                    .DefaultIfEmpty(new ObjectItem { Id = id })
    select new ObjectItem
    {
        Id = id,
        Name = sa.Name ?? ssc.Name,
        Sex = ssc.Sex,
        Age = sa.Age,
        Complexion = ssc.Complexion,
    };

edited May 23, 2017 at 12:06

CommunityBot

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answered Feb 28, 2015 at 17:24

Jeff Mercado

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4 Comments

Shittu Joseph Olugbenga Over a year ago

This answer perfectly solves my problem. So i have marked this has the correct answer.

Jeff Mercado Over a year ago

I've made a slight adjustment to the query, the left join in query syntax is needlessly complex. I've replaced it with an equivalent query.

Shittu Joseph Olugbenga Over a year ago

@frenchie: I tried your answer, but it left out the 'ObjectItem' with ID=4 from the list. That's the reason i did not accept it as the right asnwer. However, I appreciate your help.

frenchie Over a year ago

Ah yes, didn't see the lists were of different sizes!

StepUp · Accepted Answer · 2015-02-28 17:02:45Z

.Net has a function which is concatenating collections:

var concatenatedCollection = StudentWithAge.Concat(StudentWithSexAndComplexion).ToList();

        var StudentWithAge = new List<ObjectItem>()
        {
            new ObjectItem{Id=1,Name="John",Age=2},
            new ObjectItem{Id=2,Name="Smith",Age=5},
            new ObjectItem{Id=3,Name="Juliet",Age=7},   
        };

        var StudentWithSexAndComplexion = new List<ObjectItem>()
        {
            new ObjectItem{Id=1,Name="John",Sex="Male", Complexion="fair"},
            new ObjectItem{Id=2,Name="Smith",Sex="Male", Complexion=" "},
            new ObjectItem{Id=3,Name="Juliet",Sex="Female", Complexion="Blonde"},
            new ObjectItem{Id=4,Name="Shittu",Sex="Male", Complexion="fair"},
        };
        var concatenatedCollection = StudentWithAge.Concat(StudentWithSexAndComplexion).ToList();

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