AddRange take long time.

[LJN-hzleaper]

I want to add a large dataset(180000 items) to SourceList using AddRange, but AddRange takes very long time(near 1 minute). I find if I comment out following code in my view model, the AddRange will take only 20 ms. Is there any problem with my code?

MDoffDetail.FlawList.Connect() //FlawList is a SourceList to which I want add large dataset using AddRange 
.AutoRefresh(flaw => flaw.Tag)
.Filter(flaw => !b || ((FlawTag)flaw.Tag).FlawDo.UserData?.IsDeleted is not true)//filter out flaw deleted by user 
.Transform(flaw =>
{
    if (b && flaw.Tag is FlawTag tag)
    {
        flaw.Type = tag.FlawDo.UserData?.TypeSetByUser ?? tag.FlawDo.Type ?? -1;
    }

    return flaw;
})// use Transform like foreach loop to set flaw.Type property
.Bind(_observableFlawCollection) //_observableFlawCollection is an ObservableCollectionExtended<Flaw>
.Throttle(TimeSpan.FromMilliseconds(100), RxApp.TaskpoolScheduler)
.ObserveOn(RxApp.MainThreadScheduler)
.Subscribe(_ =>
{
    if (_allLeaves.Any())
        CountFlawsGroupByType();
})
.DisposeWith(d);

[LJN-hzleaper]

Removing AutoRefresh call can also reduce time taked by AddRange.