Using LINQ to get all object with the same value property?

Question

I have a list of items like this:

Item1: Id=1, Name="name1"
Item2: Id=2, Name="name1"
Item3: Id=3, Name="Test2"

What I want to perform is to get reduced list like this:

Item1: Id=1, Name="name1"
Item2: Id=2, Name="name1"

So basically I want to have items that have the same value of given property. So all the items that have the same value of given property.

I have tried to Group them but I don't know what to do next.

items.OrderBy(x => x.Name);

Edit to explain.

It seams that I did not understand the question. The Answer is expected but there is already a solution here:

Right answer!

Is your example result list correct? Shouldn't the second item be `Item2: Id=2, Name="Test2"`? — Olivier Jacot-Descombes, Sep 01 '19 at 20:29
Possible duplicate of [How to get duplicate items from a list using LINQ?](https://stackoverflow.com/questions/3811464/how-to-get-duplicate-items-from-a-list-using-linq) — Slai, Sep 01 '19 at 20:30
Your edited explanation is still a bit mysterious. The items Id=4 and 5 also have the same name. Why are they excluded? — Olivier Jacot-Descombes, Sep 02 '19 at 11:59
@OlivierJacot-Descombes You are right its my fault, misunderstanding the question. — Bojan Tomić, Sep 02 '19 at 13:10

Olivier Jacot-Descombes · Accepted Answer · 2021-03-15T19:55:15.723

Using this input ...

Item1: Id=1, Name="name1"
Item2: Id=2, Name="name1"
Item3: Id=3, Name="name3"
Item4: Id=4, Name="Test2"
Item5: Id=5, Name="name1"
Item6: Id=6, Name="name3"

... this gets all the items occurring more than once:

var result = items
    .GroupBy(x => x.Name)        // Group by name
    .Where(g => g.Count() > 1)   // Select only groups having duplicates
    .SelectMany(g => g);         // Ungroup (flatten) the groups

Result:

Item1: Id=1, Name="name1"
Item2: Id=2, Name="name1"
Item5: Id=5, Name="name1"
Item3: Id=3, Name="name3"
Item6: Id=6, Name="name3"

... this gets all the items occurring more than once and renumbers them

var result = items
    .GroupBy(x => x.Name)        // Group by name
    .Where(g => g.Count() > 1)   // Select only groups having duplicates
    .SelectMany(g => g)          // Ungroup (flatten) the groups
    .Select((x, i) => new Item { Id = i + 1, Name = x.Name });

Result:

Item1: Id=1, Name="name1"
Item2: Id=2, Name="name1"
Item3: Id=3, Name="name1"
Item4: Id=4, Name="name3"
Item5: Id=5, Name="name3"

Note that Select has an overload providing a zero-based index.

Select<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,TResult>)

However, your example input is too simplistic, therefore it is difficult to say what you expect to happen in more complex cases.

If you want entries with a specific name:

string specificName = "name1";
var result = items
    .Where(x => x.Name == specificName);

Rashid Ali · Answer 2 · 2019-09-01T20:33:22.973

3

Group items by Name, then pick first item from each group to store into reduced list:

var groupedItems = items.GroupBy(x => x.Name).Select(g => g.First()).ToList();

edited Sep 01 '19 at 20:33

answered Sep 01 '19 at 20:13

Rashid Ali

587
3
13

Using LINQ to get all object with the same value property?

2 Answers2