C# LINQ First() faster than ToArray()[0]?

Question

I am running a test.

It looks like:

method 1)

List<int> = new List<int>{1,2,4, .....} //assume 1000k
var  result ErrorCodes.Where(x => ReturnedErrorCodes.Contains(x)).First();

method 2)

List<int> = new List<int>{1,2,4, .....} //assume 1000k
var  result = ErrorCodes.Where(x => ReturnedErrorCodes.Contains(x)).ToArray()[0];

Why is method 2 is so slow compared to method 1?

Answer 1

You have a jar containing a thousand coins, many of which are dimes. You want a dime. Here are two methods for solving your problem:

1. Pull coins out of the jar, one at a time, until you get a dime. Now you've got a dime.

2. Pull coins out of the jar, one at a time, putting the dimes in another jar. If that jar turns out to be too small, move them, one at a time, to a larger jar. Keep on doing that until you have all of the dimes in the final jar. That jar is probably too big. Manufacture a jar that is exactly big enough to hold that many dimes, and then move the dimes, one at a time, to the new jar. Now start taking dimes out of that jar. Take out the first one. Now you've got a dime.

Is it now clear why method 1 is a whole lot faster than method 2?