two dimensional array with list elements

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Hi,I want to have a two dimensional array which elements are lists.

List<int>[,] dMinMax = new List<int>[3,1000];

now I want to fill the array in a for clause.for example:

dMinMax[1, 2] .Add(3);

but It gives me the error "Object reference not set to an instance of an object." on the above line.I think it means that I should build the list at first but Can I build 1000 lists? Is there a better solution? If there is no other way ,how can I build them?

Posted 29-Feb-12 7:28am

ready to learn

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3 solutions

Solution 1

A List is like an array, but it does not directly support multiple dimensions. To overcome this, you can create a List of Lists, like this:

C#

var list = new List<List<int>>();
for(int i = 0; i < 10; ++i) {
    var innerList = new List<int>();
    list.Add(innerList);
}

Posted 29-Feb-12 7:41am

Shameel

Comments

ready to learn 29-Feb-12 13:51pm

What about creating list of list of list? and how can I access to a special element?

[no name] 29-Feb-12 14:09pm

You can use the same technique to nest the List any level deep. To access an element. Check this link: http://www.dotnetperls.com/nested-list

Dr.Walt Fair, PE 29-Feb-12 15:00pm

Multiple dimension array s are fine in C#. Please don't give wrong information.

[no name] 29-Feb-12 22:29pm

Yes, they're fine. But the OP wants to know about nested lists, which are fine too. I don't see any problem using them.

Solution 2

Not sure but may be Tuple will work here:

C#

List<Tuple<int, int>> list = new List<Tuple<int, int>>();

Adding items:

C#

list.Add(new Tuple<int,int>(1, 1));

Posted 29-Feb-12 8:24am

TimGameDev

Updated 29-Feb-12 8:28am

v3

Comments

Dr.Walt Fair, PE 29-Feb-12 15:01pm

Multidimensional arrays work fine. He just forgot to initialize the List<int>.

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Dr.Walt Fair, PE · Accepted Answer · 2012-02-29T08:57:00

Your line List<int>[,] dMinMax = new List<int>[3,1000];</int></int> creates an array of list objects, which basically allocates pointer space in the array, nothing more. Then your line dMinMax[1, 2].Add(3); tries to add an item to a list that has not yet been created. In other words, if you debug you'll find that dMinMax[1, 2] is null.

Try inserting dMinMax[1, 2] = new List<int>();</int> to actually create the list before you try to add an item to it.