Removerange method after the use of take method from the list<T> has unexpected behavior

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Does anyone knows why the length after leaving the while loop body in the below code is zero?

C#

static void Main(string[] args)
		{

			var list = new List<int>();
			for (int i = 0; i < 1000; i++)
			{
				list.Add(i);
			}

			var chunks = new List<IEnumerable<int>>();

			while (list.Count > 0)
			{
				chunks.Add(list.Take(10));
				list.RemoveRange(0, 10);
			}

			int length = chunks.ToList()[0].Count();
		}

What I have tried:

I tried to chunk a list into a specific segments.

Posted 9-Oct-18 2:18am

Aydin Homay

Updated 9-Oct-18 2:54am

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Aydin Homay 9-Oct-18 8:20am

Please do not provide me chunking algorithm I already aware of several such algorithms and I know how to solve this problem. My question is only about the wired behavior of RemoverRange or perhaps Take.

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OriginalGriff · Accepted Answer · 2018-10-09T02:54:00

Linq is not magic - it works by deferred execution.
If you use the debugger, and put a breakpoint at the end of the while loop, the first time it hits it you look at chunks and it has one member - expanding the results view gives you not what you expected: 10, 11, .. 18, 19 instead of 0, 1, ... 8, 9
Run the loop again, and it gets even less what you wanted: two elements (correct) but expand either and they are both the same: 20, 21, 22, ... 28, 29
Why? Because the execution of the Take is deferred until your code attempts to use the results and by then, the source collection is empty.
So each evaluation you try to get the length gives "Enumeration yielded no results" and a length of zero.

You can do this and get the result you wanted:

chunks.Add(list.Take(10).ToList());

Because the ToList evaluates the Take immediately.

[edit] Typos.
And this: You do realize what RemoveRange actually does? And that you are using it in the least efficient way possible? Have a look at this: List<T> - Is it really as efficient as you probably think?[^] and you will see why.
[/edit]