How to create an array of List in C#?

Question

I have a problem where I need an array of arrayList.

For example if we take an Array of ArrayList of int, it will be like:

int[]<List> myData = new int[2]<List>;

myData[0] = new List<int>();
myData[0].Add(1);
myData[0].Add(2);
myData[0].Add(3);


myData[1] = new List<int>();
myData[1].Add(4);
myData[1].Add(5);
myData[1].Add(6);

myData[0].Add(7);

How can we implement a datastructure like the above in C#?

In C, its like a array of LinkedList. How can I do the same in C#?

`int[]` makes no sense sintactically. Maybe you want `List[]`? — R. Martinho Fernandes, Feb 01 '11 at 15:42
for your next question concerning C#, I would recommend to tag it with C#, because otherwise people may not find it. — Sören, Feb 01 '11 at 15:53
I know that the syntax is not supported in C# hence the question - How to do it in a different way. Thanks for C# tag recommendation. I will surely remember it. — sandyiit, Feb 03 '11 at 20:06

score 15 · Accepted Answer · answered Feb 01 '11 at 15:52

15

var myData = new List<int>[]
{
    new List<int> { 1, 2, 3 },
    new List<int> { 4, 5, 6 }
};

answered Feb 01 '11 at 15:52

QrystaL

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Thanks Qrystal, This is the solution I needed. – sandyiit Feb 03 '11 at 20:13
1

You don't need "List" -- var myData = new[] { new List { 1, 2, 3 }, new List { 4, 5, 6 } }; – onuralp Jul 24 '13 at 10:56

Sören · Answer 2 · 2011-02-01T15:48:51.070

10

Almost as you tried, only the first line is incorrect:

List<int>[] myData = new List<int>[2];
myData[0] = new List<int>();
myData[0].Add(1);
myData[0].Add(2);
myData[0].Add(3);


myData[1] = new List<int>();
myData[1].Add(4);
myData[1].Add(5);
myData[1].Add(6);

myData[0].Add(7);

Thanks to madmik3, here is a link you can read something about generic lists in C#: click me

Also, if you want to read something about arrays, e.g. the static copy method of the Array class, here is some link for that.

edited Feb 01 '11 at 15:48

answered Feb 01 '11 at 15:41

Sören

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1

This answer is right but the asker should also take a little time to earn more about Collections and Generics in C#. You will use the all the time so learning them will help a ton. You can start with list like above here: http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx – madmik3 Feb 01 '11 at 15:44

score 4 · Answer 3 · answered Feb 01 '11 at 15:41

4

var arraySize = 2;
var myArray = new List<Int32>[arraySize];


myArray[0] = new List<Int32>();
myArray[1] = new List<Int32>();
// And so on....

myArray[0].Add(5);

answered Feb 01 '11 at 15:41

Chris Shain

50,833
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Thanks Chris, This is the solution I needed. – sandyiit Feb 03 '11 at 20:13

score 3 · Answer 4 · edited Feb 01 '11 at 15:49

3

I prefer lists but it's up to you...

List<List<int>> lst = new List<List<int>>();

lst.Add(new List<int>());
lst.Add(new List<int>());

lst[0].Add(1);
lst[1].Add(1);
lst[1].Add(2);
lst[0].Add(5);

Then if you really want a list at the end of it all use some linq.

lst.ToArray();

edited Feb 01 '11 at 15:49

R. Martinho Fernandes

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answered Feb 01 '11 at 15:44

Hawxby

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C# is case sensitive, and `List` methods (like everything in the BCL) are PascalCased. – R. Martinho Fernandes Feb 01 '11 at 15:47
Bah, copy and paste typo. Thanks for fixing it – Hawxby Feb 01 '11 at 16:06

score 1 · Answer 5 · answered Feb 01 '11 at 15:40

You're trying to take the concrete type List<int> and make an array of it.
Just like string becomes new string[2], so to List<int> becomes new List<int>[2].

This will create an array which can hold two List<int>s.
However, each element in the array starts out null.
You'll need to put a new List<int>() into each slot of the array before using it.

However, you should probably use a List<List<int>> instead of an array of lists.

How to create an array of List in C#?

5 Answers5

Linked