CODEWITHSUNDEEP
c#linqcoding-style
Otiel
Otiel

Reputation: 18743

Copy a list of objects to another typed list in one line of code

I have a List of MyType1 objects. I want to copy all these objects in a new List of MyType2 objects, having a constructor for MyType2 that takes a MyType1 object as argument.

For now, I do it this way:

List<MyType1> type1objects = new List<MyType1>();
// Fill type1objects
// ...
List<MyType2> type2objects = new List<MyType2>();
foreach (MyType1 type1obj in type1objects) {
    MyType2 type2obj = new MyType2(type1obj);
    type2objects.Add(type2obj);
}

Is there a way to do this one-line (I'm thinking maybe it is possible with Linq)?

Upvotes: 3

Views: 152

Answers (7)

James Johnson
James Johnson

Reputation: 46047

You should be able to do something like this:

List<MyType2> list2 = new List<MyType2>(list1.Select(x => new MyType2(x)));

Upvotes: 0

xanatos
xanatos

Reputation: 111870

List<MyType2> type2objects = new List<MyType2>();
type2objects.AddRange(type1objects.Select(p => new MyType2(p)));

In this way you can even preserve the values contained in type2objects.

I'll add that you know the size of type1objects, so you can speedup a little:

List<MyType2> type2objects = new List<MyType2>(type1objects.Count);

Here the capacity of type2objects is pre-setted.

or, if you are re-using an "old2" type2objects

if (type2objects.Capacity < type1objects.Count + type2objects.Count)
{
    type2objects.Capacity = type1objects.Count + type2objects.Count;
}

In this way you know the List won't need intermediate resizes.

Someone will call this premature optimization, and it is. But you could need it.

Upvotes: 0

user645280
user645280

Reputation:

You might also get some mileage out of Convert.ChangeType() depending on what you're converting:

List<MyType2> type2objects = type1objects.Select(
    type1object => Convert.ChangeType(type1object, typeof(MyType2))
    ).ToList();

Upvotes: 0

Fischermaen
Fischermaen

Reputation: 12458

If you just copy all elements from list1 to list2 you will not get true copies of those elements. You will just have another list with the same elements!!!

Upvotes: 0

Mohamed Abed
Mohamed Abed

Reputation: 5113

var type2objects = type1objects.Select(type1obj => new MyType2(type1obj)).ToList();

Upvotes: 1

BrokenGlass
BrokenGlass

Reputation: 160912

You can use a simple projection using Select() with Linq, then make a list out of this enumeration using ToList():

var type2objects = type1objects.Select( x => new MyType2(x))
                               .ToList();

Upvotes: 3

Ilia G
Ilia G

Reputation: 10211

var type2objects = type1objects.Select(o => new MyType2(o)).ToList();

Upvotes: 7

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