Easy way to copy a List<List<T>>

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Sin Jeong-hun - 28 Jul 2006 18:23 GMT

List<List<T>> a=param;
List<List<T>> b=a;
If I change b, then a is get changed. I want another copy of a, that is
completely independent of a. I used double-nested for loop to copy each
element manually. Is there any more efficent way to do that? Something
like,
List<List<T>> b=CreateClone(a);

Thanks.

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Nicholas Paldino [.NET/C# MVP] - 28 Jul 2006 18:39 GMT

Sin Jeong-hun,

The easiest way to do this would be to use the ConvertAll method on the
instance itself. You can always convert the list to itself. =)

So, you can do:

// This assumes T is a valid type.
List<List<T>> a = param;

// Make a copy.
List<List<T>> b = a.ConvertAll(delegate(T input) { return input; });

Basically, you are passing the value through to a new list.

Hope this helps.

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- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard.caspershouse.com

> List<List<T>> a=param;
> List<List<T>> b=a;
[quoted text clipped - 5 lines]
>
> Thanks.

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Sin Jeong-hun - 28 Jul 2006 19:20 GMT

Thank you all!

> Sin Jeong-hun,
>
[quoted text clipped - 26 lines]
> >
> > Thanks.

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Jon Shemitz - 28 Jul 2006 19:56 GMT

> // Make a copy.
> List<List<T>> b = a.ConvertAll(delegate(T input) { return input; });

This won't compile - you need to write "ConvertAll<List<T>>". More
importantly, this only clones the 'outer list' - you get a new list of
the same inner List<T> elements. If you want a wholly independent copy
(so that changing one of the lists in the original tree doesn't affect
the copy) you need

List<List<T>> DeepCopy =
List.ConvertAll<List<T>>(delegate(List<T> Branch)
{
return Branch.ConvertAll<T>(delegate(T Leaf){return Leaf;});
});

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kjetil.gloppen@gmail.com - 25 Aug 2006 09:51 GMT

> List<List<T>> DeepCopy =
> List.ConvertAll<List<T>>(delegate(List<T> Branch)
> {
> return Branch.ConvertAll<T>(delegate(T Leaf){return Leaf;});
> });

If T is a reference type, this method will still not be "deep" enough.
The leafs will just be refering to the same objects. To fix this I
guess you could make sure T inmplementes ICloneable and let Clone()
return a deap copy of T. Then the code should be:

List<List<T>> DeepCopy =
List.ConvertAll<List<T>>(delegate(List<T> Branch)
{
return Branch.ConvertAll<T>(delegate(T Leaf){return
Leaf.Clone();});
});

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Easy way to copy a List<List<T>>

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