Diff between two arraylists can't read except

Question

1.89/5 (3 votes)

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C#

public static void diff(ArrayList args)
      {
          if (args.Count < 2 || args.Count > 3)
          {
              Console.WriteLine("Insufficent Number of Args");
          }
          else if (args.Count == 3)
          {
              string source_path = get_abs_path(args[1].ToString());
              StreamReader sr = new StreamReader(source_path);
              ArrayList text1 = new ArrayList();
              string [] file = sr.ReadToEnd().Split('\n');
              foreach (string line in file)
              {
                  text1.Add(line);
              }
              sr.Close();
              Console.WriteLine("Content of " + source_path + " :");
              Console.WriteLine(file);

              source_path = get_abs_path(args[2].ToString());
              sr = new StreamReader(source_path);
              ArrayList text2 = new ArrayList();
              string[] file2 = sr.ReadToEnd().Split('\n');
              foreach (string lin in file2)
              {
                  text2.Add(lin);
              }
              sr.Close();
              ArrayList difference = new ArrayList(text1.Except(text2)); // what is the problem here !

          }
      }

Posted 10-Nov-13 3:39am

Shta

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Comments

CHill60 10-Nov-13 9:44am

Use the Improve question link to add some details ... for example the problem that you are having

Sergey Alexandrovich Kryukov 10-Nov-13 13:18pm

To start with, stop using obsolete ArrayList, use System.Collections.Generic.List<>.
—SA

2 solutions

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OriginalGriff · Accepted Answer · 2013-11-10T03:53:00

The message is accurate:

'System.Collections.ArrayList' does not contain a definition for 'Except' and no extension method 'Except' accepting a first argument of type 'System.Collections.ArrayList' could be found (are you missing a using directive or an assembly reference?)

But not that helpful.

Basically, you shouldn't be using ArrayList - it's out of date, and was replaced by the Generic collection types nearly ten years ago!

ArrayLists do not support the IEnumerable<T> interface, which allows them to use Linq extension methods. Replace your ArrayList's with List<string> instead and it should work fine.

-------OFF TOPIC ANSWER SECTION-------

"There is something confusing me in what you wrote in your solution: "ArrayLists do not support the IEnumerable interface, which allows them to use Linq extension methods."
I think it should be: "ArrayLists do not support the IEnumerable interface, which would allow them to use Linq extension methods." or maybe "ArrayLists do not support the IEnumerable interface, which prevents you from using Linq extension methods on them."
Cheers!"

Ah! It's understandable, but...
There are two Interfaces involved here: IEnumerable (the old one, that allows you to use foreach loops) and IEnumerable<T> the newer, strongly typed generic version introduced at .NET V2.0

The former is not the same (and IEnumerable<T> derives from IEnumerable) and only the latter will work with Linq methods, because they are all predicated upon IEnumerable<T> - if you look at the MSDN description for a link method: http://msdn.microsoft.com/en-us/library/system.linq.enumerable.except(v=vs.110).aspx[^] it is an IEnumerable<T> method, not IEnumerable.

Try it:

C#

public class enumableObject : IEnumerable
    {
    public IEnumerator GetEnumerator()
        {
        throw new NotImplementedException();
        }
    }
public class enumerableGeneric<T> : IEnumerable<T>
    {
    public IEnumerator<T> GetEnumerator()
        {
        throw new NotImplementedException();
        }

    IEnumerator IEnumerable.GetEnumerator()
        {
        throw new NotImplementedException();
        }
    }

Then

C#

List<string> list = new List<string>();
var x = list.Except(list);

Works fine

C#

enumerableGeneric<string> eg = new enumerableGeneric<string>();
var z = eg.Except(eg);

Works fine

C#

enumableObject eo = new enumableObject();
var y = eo.Except(eo);

Gives a compilation error:

MyNamespace.frmMain.enumableObject' does not contain a definition for 'Except' and no extension method 'Except' accepting a first argument of type 'MyNamespace.frmMain.enumableObject' could be found (are you missing a using directive or an assembly reference?)

Exactly the same as a ArrayList.

Sampath Lokuge · Accepted Answer · 2013-11-10T03:57:00

Solution 2

The Except method returns IEnumerable, you need to convert the result to list:

C#

list1 = list1.Except(list2).ToList();

Convert ArrayList to List:

XML

using System;
using System.Collections;
using System.Collections.Generic;

static class Extensions
{
    /// <summary>
    /// Convert ArrayList to List.
    /// </summary>
    public static List<T> ToList<T>(this ArrayList arrayList)
    {
    List<T> list = new List<T>(arrayList.Count);
    foreach (T instance in arrayList)
    {
        list.Add(instance);
    }
    return list;
    }
}

class Program
{
    static void Main()
    {
    // Create ArrayList.
    ArrayList arrayList = new ArrayList();
    arrayList.Add(1);
    arrayList.Add(2);
    arrayList.Add(3);

    // Use extension method.
    List<int> list = arrayList.ToList<int>();
    foreach (int value in list)
    {
        Console.WriteLine(value);
    }
    }
}

Output:

1
2
3

I hope this will help to you.

Posted 10-Nov-13 3:57am

Sampath Lokuge

Updated 10-Nov-13 4:07am

v3

Comments

OriginalGriff 10-Nov-13 10:01am

Reason for my vote of one: If you read the question, you will find that the OP is not using generic classes - he is using the much older ArrayList collection - which do not support LINQ methods...

Sampath Lokuge 10-Nov-13 10:09am

If you want,You can convert ArrayList into List by using Extension method.Please see my answer.I hope you change your vote :)

OriginalGriff 10-Nov-13 10:12am

Sorry, but that is what we call "A Massive Bodge" - especially when compared to not using an ArrayList in the first place!

BillWoodruff 10-Nov-13 11:36am

Hi Og, forgive me for getting etymological on you, but I am fascinated by the term "massive bodge" which, to my knowledge, doesn't occur in American slang. The "classic" definition seems to be some kind of pejorative reference to a swollen, or unusually large, nose. But, it has the meanings of a "big mess," in general ? Possibly a meaning similar to "kludge," meaning an inelegant, messy, patching together of something to get it working ?

OriginalGriff 10-Nov-13 11:54am

A "bodge" is a "kludge" that you have beaten repeatedly with a large hammer in order to fit it into a hole for which it is the incorrect shape. And then glued the bits that fell off back on to make it look like nothing happened.