When should I use a List vs a LinkedList


Question

When is it better to use a List vs a LinkedList?

2
363
8/30/2018 2:14:04 PM

Accepted Answer

Edit

Please read the comments to this answer. People claim I did not do proper tests. I agree this should not be an accepted answer. As I was learning I did some tests and felt like sharing them.

Original answer...

I found interesting results:

// Temporary class to show the example
class Temp
{
    public decimal A, B, C, D;

    public Temp(decimal a, decimal b, decimal c, decimal d)
    {
        A = a;            B = b;            C = c;            D = d;
    }
}

Linked list (3.9 seconds)

        LinkedList<Temp> list = new LinkedList<Temp>();

        for (var i = 0; i < 12345678; i++)
        {
            var a = new Temp(i, i, i, i);
            list.AddLast(a);
        }

        decimal sum = 0;
        foreach (var item in list)
            sum += item.A;

List (2.4 seconds)

        List<Temp> list = new List<Temp>(); // 2.4 seconds

        for (var i = 0; i < 12345678; i++)
        {
            var a = new Temp(i, i, i, i);
            list.Add(a);
        }

        decimal sum = 0;
        foreach (var item in list)
            sum += item.A;

Even if you only access data essentially it is much slower!! I say never use a linkedList.




Here is another comparison performing a lot of inserts (we plan on inserting an item at the middle of the list)

Linked List (51 seconds)

        LinkedList<Temp> list = new LinkedList<Temp>();

        for (var i = 0; i < 123456; i++)
        {
            var a = new Temp(i, i, i, i);

            list.AddLast(a);
            var curNode = list.First;

            for (var k = 0; k < i/2; k++) // In order to insert a node at the middle of the list we need to find it
                curNode = curNode.Next;

            list.AddAfter(curNode, a); // Insert it after
        }

        decimal sum = 0;
        foreach (var item in list)
            sum += item.A;

List (7.26 seconds)

        List<Temp> list = new List<Temp>();

        for (var i = 0; i < 123456; i++)
        {
            var a = new Temp(i, i, i, i);

            list.Insert(i / 2, a);
        }

        decimal sum = 0;
        foreach (var item in list)
            sum += item.A;

Linked List having reference of location where to insert (.04 seconds)

        list.AddLast(new Temp(1,1,1,1));
        var referenceNode = list.First;

        for (var i = 0; i < 123456; i++)
        {
            var a = new Temp(i, i, i, i);

            list.AddLast(a);
            list.AddBefore(referenceNode, a);
        }

        decimal sum = 0;
        foreach (var item in list)
            sum += item.A;

So only if you plan on inserting several items and you also somewhere have the reference of where you plan to insert the item then use a linked list. Just because you have to insert a lot of items it does not make it faster because searching the location where you will like to insert it takes time.

97
9/2/2015 4:13:21 PM

Exper Answer

In most cases, List<T> is more useful. LinkedList<T> will have less cost when adding/removing items in the middle of the list, whereas List<T> can only cheaply add/remove at the end of the list.

LinkedList<T> is only at it's most efficient if you are accessing sequential data (either forwards or backwards) - random access is relatively expensive since it must walk the chain each time (hence why it doesn't have an indexer). However, because a List<T> is essentially just an array (with a wrapper) random access is fine.

List<T> also offers a lot of support methods - Find, ToArray, etc; however, these are also available for LinkedList<T> with .NET 3.5/C# 3.0 via extension methods - so that is less of a factor.

260
11/12/2013 8:28:28 PM

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