Thread: Accessing Different "Levels" of ArrayList

Hi,

Can anyone help me with the syntax to access different levels of an ArrayList?

Something like:

Code:

rawData[0]          [0]    [0]
                           [1]
                    [1]    [0]
                           [1]
                           [2]
                           [3]
                    [2]    [0]
                           [1]
                           [2]
                    [3]    [0]
                           [1]
                           [2]
                           [3]
                           [4]

where each column to the right is another "Level"

Thanks.
Steve

If it's a multi-dimensional array, you access members as list[0,2,1]. If it's a jagged array, you access members as list[0][2][1].

>If it's a multi-dimensional array
It's an ArrayList object.

>If it's a jagged array
It's an ArrayList object. Neither of those solutions will work unless he wants to call the ToArray method, which is exceptionally wasteful.

>Can anyone help me with the syntax to access different levels of an ArrayList?
Something like this?

Code:

namespace jsw {
    using System;
    using System.Collections;

    public class Test {
        public static void Main()
        {
            ArrayList al = new ArrayList();

            // Build a 5x5 ArrayList
            for (int i = 0; i < 5; i++) {
                al.Add(new ArrayList());

                for (int j = 0; j < 5; j++)
                    ((ArrayList)al[i]).Add(i * j + 1);
            }

            // Display the table
            foreach (ArrayList row in al) {
                foreach (int item in row)
                    Console.Write("[{0,2}]", item);
                Console.WriteLine();
            }

            // Get the item at index [2][3]
            int item2 = (int)((ArrayList)al[2])[3];

            Console.WriteLine("At index [2][3]: {0}", item2);
        }
    }
}

An ArrayList of ArrayLists is conceptually the same as a jagged array, and you're indexing it exactly the same as I said you should, with the exception of casting. I can see that it could be confusing trying to index into that sort of structure since you have to cast all over the place. If you use generic lists instead of ArrayList, you don't have that problem.

>An ArrayList of ArrayLists is conceptually the same as a jagged array
Conceptually, yes. But your suggestion failed to mention that you were talking in the abstract.

Originally Posted by stevespai

pianorain: I know should use generic lists, just trying to learn ArrayList also

I almost never object to someone learning something, but, in my personal opinion, ArrayList ranks right up there with gets(). There is no time when you should prefer ArrayList over a generic list; only use ArrayList if you have to run on the .Net 1.1 runtime. There are small performance differences between the two (ArrayList is generally slower because of the constant casting and boxing of value types, but generic lists are slower to create), but the type-safeness of generic lists just helps you avoid so many other errors. For instance, it's a lot easier to write code that accidently inserts an int into an ArrayList rather than into a generic list. You won't catch the ArrayList error until you get a run-time cast error from the int, while the generic list error will fail at compile-time.

>but, in my personal opinion, ArrayList ranks right up there with gets().
It makes sense to understand the workings of both, whether they're recommended or not. ArrayList is very common in older C# code, and still pretty common in newer code too.