.Net C# Ascending sort of ArrayList with Hashtables

[Cappamontana]

Hi,

I'm stuck with a problem...in .Net C# I want to sort an ArrayList containing Hashtables. The sort key must be the key of the Hashtable. How can I do this?

I've coded some example here...

ArrayList arr = new ArrayList();
Hashtable row = new Hashtable();
Hashtable row2 = new Hashtable();
row.Add("name", "Naomi Watts");
row.Add("age", "24");
row2.Add("name", "Scarlett Johanson");
row2.Add("age","16");
arr.Add(row);
arr.Add(row2);
 

Now consider that I want to sort the ArrayList ascending on row["age"].
Sorting on IComparer works only when sorting on Objects, and I can't find a way for this situation.

[Shashi Sadasivan]

You should be typecasting the object back to a hash table type

cheers.
PS: your structure dosent look so good!

[Cappamontana]

How can I do that? Simply by "(Hashtable)..." or "as Hashtable"? Can you give an example please? And whats wrong with the structure? How would you do it in a situation where you have to save columns and rows?

[Plater]

IComparer interface has two objects come in, that you then type-cast to the object for sorting purposes.

As for your structure, there seems to be a lot of problems.
you are only using ONE hastable, never creating another one. So your arraylist is just going to have the same hastable in it everytime.

It rather seems that a DataTable would be more useful to you in this situation (define some colums, add values in a row) So instead of a new hashtable each time, you would just add another row to your DataTable.

[Cappamontana]

Yes I saw it, thanks...It was only a sample code and in the actual source it's written right. I changed it now in the post. I could have use DataTables but me was said that this is a much faster solution :S

I will try to typecast and see if it works, thanks!

[Cappamontana]

Small problem left :D don't know how to fill in the arr.Sort(...) and if it will work like this.

Thank you!

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
 
namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            ArrayList arr = new ArrayList();
            Hashtable row = new Hashtable();
            Hashtable row2 = new Hashtable();
            row.Add("name", "Naomi Watts");
            row.Add("age", "24");
            row2.Add("name", "Scarlett Johanson");
            row2.Add("age", "16");
            arr.Add(row);
            arr.Add(row2);
 
            Array.Sort();   <----- How dow I fill this in?
        }
    }
 
    class sortAscending : IComparer
    {
       int IComparer.Compare(object a, object b)
       {
           //Typecast the object to Hashtables
          Hashtable c1 = (Hashtable)a;
          Hashtable c2 = (Hashtable)b;
          if (Int32.Parse(c1["age"].ToString()) > Int32.Parse(c2["age"].ToString()))
             return 1;
         if (Int32.Parse(c1["age"].ToString()) < Int32.Parse(c2["age"].ToString()))
             return -1;
          else
             return 0;
       }
 
        public static IComparer sortAsc()
        {
            return (IComparer)new sortAscending();
        }
 
    }
}
 

[Plater]

Try this:

Array.Sort(arr, new sortAscending());
 

You don't need that static method in your sortAscending class.

[Cappamontana]

Sorry, won't work...

1.The best overloaded method match for 'System.Array.Sort(System.Array, System.Array)' has some invalid arguments \Projects\test\Program.cs 22 13 test
2.Argument '1': cannot convert from 'System.Collections.ArrayList' to 'System.Array' \Projects\test\Program.cs 22 24 test
3.Argument '2': cannot convert from 'test.sortAscending' to 'System.Array' \Projects\test\Program.cs 22 29 test

[Plater]

Ooooo it's mad because of that, hehe oops

arr.Sort(new sortAscending());
 

[Cappamontana]

LOL! Plater it keeps complaining :(

1.The best overloaded method match for 'System.Array.Sort(System.Array)' has some invalid arguments \Projects\test\Program.cs 22 13 test
2.Argument '1': cannot convert from 'void' to 'System.Array' \Projects\test\Program.cs 22 24 test

[Plater]

You put in "arr" and not "Array" before the .Sort() right?

[Cappamontana]

:$ sorry ... It now works perfectly! This surely made me learn a bit about IComparer. Thank you for your help!