C＃从“锯齿状”列表中删除列表

Question

I'm trying to remove a List<int> from a List<List<int>> , I've looked everywhere and haven't found a solution.

Here's what I've tried so far:

List<List<int>> my2DList = ... ;  // this is where I assign my 2D list
my2DList.Remove(new List<int>( ... ));

But my2DList 's length stays the same. What should I do?

Answer 1

The problem is that List<int> doesn't override Equals / GetHashCode , so your new list is never equal to the existing one. (Basically, it will be comparing references rather than contents.)

Three options:

• Find the exact list you want to remove, and pass that reference to Remove
• Find the index of the list you want to remove, and pass that to RemoveAt
• Create a predicate and use RemoveAll

An example of the last one:

List<int> listToRemove = new List<int> { ... };
my2DList.RemoveAll(x => x.SequenceEqual(listToRemove));

Answer 2

You need to remove the exact object you want to remove, not a new object (which would be a different object). So for example:

my2DList.Remove(my2DList[3]);

If you do not know the index, or the object, you'd need to iterate over the List to find the correct object.