C# performance: construct new collection with existing items using constructor or loop?

Question

I've searched but not found answer, maybe because this question is not easy to describe. For example in WPF, I have a model Test, and a List<Test> lst, then have to construct a ObservableCollection<TestViewModel> ObsTests. There maybe 2 ways:

var ObsTests = new ObservableCollection<TestViewModel>(lst
    .Select(t = > new TestViewModel(t));

var ObsTests = new ObservableCollection<TestViewModel>();
foreach(var test in lst)
{
    ObsTests.Add(new TestViewModel(test));
}

Please tell me which is better in performance, and tell me the best solution if AsParallel is available(such as is ObservableCollection threadsafe? I'm using .net 4.5)

Hint: if you have a performance issue; then start profiling. If you don't have a perfomance issue; then focus on writing easy-to-read code. — GhostCat, Jun 28 '16 at 09:36
I have performance issue, but there are too many combinations, adding parallel for example, and I think it is a valuable common question for all developers. — Lei Yang, Jun 28 '16 at 09:39
First and second approaches are identical in performance. When you pass in collection into ObservableCollection it performs foreach loop inside in ctor. — Karolis Kajenas, Jun 28 '16 at 09:43
You might want to look at System.Threading.Tasks.Parallel.ForEach (https://msdn.microsoft.com/en-gb/library/system.threading.tasks.parallel(v=vs.110).aspx) or AsParallel which in some cases can improve performance. — apc, Jun 29 '16 at 14:43
@apc I already know that. but there are too many choices for Task, Parellel, even regarding Parellel, there are ForAll, Foreach... — Lei Yang, Jun 30 '16 at 01:01

score 2 · Accepted Answer · edited May 23 '17 at 12:32

2

There is no difference. Ctor uses Add method from base class Collection: Reffer: click!

public ObservableCollection(List<T> list)
    : base((list != null) ? new List<T>(list.Count) : list)
{
    CopyFrom(list);
}

private void CopyFrom(IEnumerable<T> collection)
{
    IList<T> items = Items;
    if (collection != null && items != null)
    {
        using (IEnumerator<T> enumerator = collection.GetEnumerator())
        {
            while (enumerator.MoveNext())
            {
                items.Add(enumerator.Current);
            }
        }
    }
}

ObservableCollection basis on Collection so it is not thread-safe. For thread-safe collection - use some class from Concurrent namespace. More on MSDN.

You can also implement own-super-fast observable collection. Like here: Click!

edited May 23 '17 at 12:32

Community

1
1

answered Jun 28 '16 at 09:41

pwas

3,225
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Then is there a Concurrent collection which implements **INotifyCollectionChanged**? – Lei Yang Jun 28 '16 at 09:44
No - but see my last words - i have added link to custom implementation. – pwas Jun 28 '16 at 09:45
how do you consider **Parallel** here? will it improve(and how)? – Lei Yang Jun 28 '16 at 09:53

score -1 · Answer 2 · answered Jun 28 '16 at 09:44

-1

In case if you have standard implementation of some action, and can do the same using your code, it is better to choose the standard implementation. Also it looks more tiny :)

answered Jun 28 '16 at 09:44

Waldemar

5,363
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What you say seems to apply to all questions. – Lei Yang Jun 28 '16 at 09:45

C# performance: construct new collection with existing items using constructor or loop?

2 Answers2