LINQ SequenceEqual returns false but comparing using Except gives different result-CodePudding

I have two lists that I believe to be equal and in same sequence, but when I run SequenceEqual() it is returning false. See below for pseudo example:

// For brevity’s sake assume the two-list data is as follows
List<string> list1 = new List<string> {"1", "2", "3"};
List<string> list2 = new List<string> {"1", "2", "3"};

list1.SequenceEqual(list2); // returning false
list1.Except(list2).Count(); // returning 0
list2.Except(list1).Count(); // returning 0

In reality my list data is much larger (~ 8000 items), but I am confused why I would get 0 for both Except().Count() yet false for SequenceEqual()?

Edit: Added Count to the Except examples.

CodePudding user response：

You do different comparisons. As for Except it

Removes duplicates
Doesn't take order of items into account
Ignores items which are in the second argument if they are not present in the first

that's why

// Duplicated "2" will be ignored
List<string> list1 = new List<string>() { "1", "2", "3", "2" };
// Duplicated "3" will be ignored
// Order doesn't matter
// "7777777" will be ignored
List<string> list2 = new List<string>() { "3", "3", "1", "2", "7777777"};

// 0; since all items within list1 - "1", "2", "3"
// are in the list2, duplicates ignored
int count = list1.Except(list2).Count();

When SequenceEqual returns true if and only if sequences are equal order and duplicates matter. In the example above SequenceEqual returns false since list1.Count != list2.Count, list1[0] != list2[0] etc.