Embarrassing code admission of the day (or why C.S. is good for you)

[GParkings]

yes. list being the simplest data type in which an order is applied to a set of data Though, judging by your rep scores on here you are more likely to know what you are talking about than I am, so ... am i missing something here, do we work in different languages with different concepts of 'list'? should we be using

list.ElementAt(0)

instead?

Pedis ex oris Quidquid latine dictum sit, altum sonatur

[Mladen Jankovic]

Yes it is, But also it has O(n) complexity.

[Pete OHanlon]

Took me a moment or two to spot that. Couldn't really see it until I thought it through. Good catch - how did you find it? For others - what happens when you remove at 0? How is this handled in terms of resizing when you remove from the start of the list. As a comparison, remove from the last position instead (ok, it's not the same logical code, but it shows timings).

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"Mind bleach! Send me mind bleach!" - Nagy Vilmos

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[Pete OHanlon]

It's not a bug per se, it's an efficiency thing.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility

[Xiangyang Liu]

Ennis Ray Lynch, Jr. wrote:

Another Hint: Run it with a populated list of 100,000 elements and check the timing. There is a particular feature of this data structure that happens with this particular code that one small change would avoid.

But that is not called a bug, is it?

My Younger Son & His "PET"

[Pete OHanlon]

Didn't think that deserved a 1. Corrected. As a hint, the answer has to do with which side of the list you remove the element from. How is it handled re, resizing?

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility

[_Zorro_]

Oh, what would be a better approach? ElementAt? I thought it would be the same...

[Keith Barrow]

Ah. Now you see, that is another example as to why programming is hard.

Sort of a cross between Lawrence of Arabia and Dilbert.[^]
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A Dead ringer for Kate Winslett[^]

[Claude Martel Olivier]

Not sure if it's intended or not but you're going to delete the list by deleting the first item over and over?

[_Zorro_]

Pete O'Hanlon wrote:

what happens when you remove at 0? How is this handled in terms of resizing when you remove from the start of the list

I see it now, thank's!

[Julien Villers]

When n = 0, you could have an exponential cost, it wouldn't matter much, now would it?

'As programmers go, I'm fairly social. Which still means I'm a borderline sociopath by normal standards.' Jeff Atwood 'I'm French! Why do you think I've got this outrrrrageous accent?' Monty Python and the Holy Grail

[Julien Villers]

Yes it is! http://www.codinghorror.com/blog/2011/06/performance-is-a-feature.html[^]

'As programmers go, I'm fairly social. Which still means I'm a borderline sociopath by normal standards.' Jeff Atwood 'I'm French! Why do you think I've got this outrrrrageous accent?' Monty Python and the Holy Grail

[Pete OHanlon]

Basically, one way or the other there's a 0(n) operation - either in finding the element at position n, or removing the element at position n. Removing the element at n where n = 0 would, at first glance, appear to be a good optimisation. Unfortunately, it has side effects.

*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington

"Mind bleach! Send me mind bleach!" - Nagy Vilmos

My blog | My articles | MoXAML PowerToys | Mole 2010 - debugging made easier - my favourite utility

[Mladen Jankovic]

Unless the actual implementation of the algorithm starts iterating from the end of the list, from some strange reason.

[Dario Solera]

No, it's O(1) (because there's an array behind): http://msdn.microsoft.com/en-us/library/0ebtbkkc.aspx[^]

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[V 0]

Sorry, can't find anything wrong. The only thing I see on sight is you manipulate the size of a list while looping it. This is potentially dangerous, depending on what you do with it.

		Random r = new Random((int) DateTime.Now.Ticks);			
		List fakelist = new List();
		
		Console.WriteLine("Populating list");
		for(int i = 0; i < 100000; i++){
			fakelist.Add(r.NextDouble() + i);
		}												//end for
		
		Console.WriteLine("looping list, writing to file");
		System.IO.StreamWriter writer = new System.IO.StreamWriter(@"C:\\temp\\fakelist.txt");
		int index = 0;
		while(fakelist.Count > 0){
			double temp = fakelist\[0\];
			writer.Write(temp);
			writer.Write("\\t");
			if(index%10 == 0){
				writer.WriteLine("");
				writer.WriteLine(DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss:ffff"));
				writer.WriteLine("");
			}											//end if
			writer.Flush();
			index++;
			fakelist.RemoveAt(0);
		}												//end while
		Console.WriteLine("Done!");
		writer.Close();			

		Console.WriteLine("Press enter to quit.");
		Console.ReadLine();

V.

[Julien Villers]

Well, in .NET a List is well documented, so list[0] should be O(1), while list[n-1] is also 0(1) (see post below for MSDN link). A .NET List is supposed to be a dynamic array, with the expected performance of an array for single element access. So reversing the loop shown here would not even cause the access speed to be bad, but even if it were bad, it would not be as bad as the constant resizing (RemoveAt(0)) would be. Morality: use a Queue (or not).

'As programmers go, I'm fairly social. Which still means I'm a borderline sociopath by normal standards.' Jeff Atwood 'I'm French! Why do you think I've got this outrrrrageous accent?' Monty Python and the Holy Grail

[Mladen Jankovic]

I'm not familiar with internals of List<> in .Net. I was under assumption that it is implemented as plain vanilla list in which case the removal of either head or tail should consume the same amount of time, but your hint tells me that it isn't usual list.

[GParkings]

IIRC its an extension method so very likely to be the same as it will be using the pre-existing public members unless of course there's some IL magic going on...

Pedis ex oris Quidquid latine dictum sit, altum sonatur

[TheGreatAndPowerfulOz]

Technically, it "works". But, if you also define working as being the most reasonably efficient, then yes it it is a bug.

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