Does LINQ to Objects keep its order

Question

I have a List<Person> and instead want to convert them for simple processing to a List<string>, doing the following:

List<Person> persons = GetPersonsBySeatOrder();
List<string> seatNames = persons.Select(x => x.Name).ToList();

Console.WriteLine("First in line: {0}", seatNames[0]);

Is the .Select() statement on a LINQ to Objects object guaranteed to not change the order of the list members? Assuming no explicit distinct/grouping/ordering is added

Also, if an arbitrary .Where() clause is used first, is it still guaranteed to keep the relative order, or does it sometimes use non-iterative filtering?

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As Fermin commented above, this is essentially a duplicate question. I failed on selecting the correct keywords to search stackoverflow

Preserving order with LINQ

Answer 1

In current .Net implementation it use such code. But there are no guarantee that this implementation will be in future.

private static IEnumerable<TResult> SelectIterator<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, int, TResult> selector)
{
  int index = -1;
  foreach (TSource source1 in source)
  {
    checked { ++index; }
    yield return selector(source1, index);
  }
}

Answer 2

It depends on the underlying collection type more than anything. You could get inconsistent ordering from a HashSet, but a List is safe. Even if the ordering you want is provided implicitly, it's better to define an explicit ordering if you need it though. It looks like you're doing that judging by the method names.