Sorting an Array

[Ennis Ray Lynch Jr]

public class Foo : Comparer<foo> { private string mMyString = new string('c', 100); public override int Compare(Foo one, Foo two) { return one.mMyString.Substring(59).CompareTo(two.mMyString.Substring(59)); } } Use System.Collections.Generic.List as the list. Also, you may have to vary the code in the Compare method as I did not bother to test it.

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[Guffa]

A comparer is pretty simple. It's just a class with a Compare method that works like any other Compare method (like string.Compare for example). Try this:

class SubstringComparer : IComparer<string> {
private int _offset, _len;
public SubstringComparer(int offset, int len) { _offset = offset; _len = len; }
public override int Compare(string x, string y) {
return string.Compare(x, _offset, y, _offset, _len);
}
}

Array.Sort(myArray, new SubstringComparer(59, int.MaxValue));

modified on Saturday, December 08, 2007 2:31:24 PM

[electriac]

This is my code that will not compile. class SubstringComparer : IComparer<string> { private int _offset, _len; public SubstringComparer(int offset, int len) { _offset = offset; _len = len; } public override int Compare(string x, string y) //--------------------------------------------------------- // I get no suitable method found to override Compare //--------------------------------------------------------- { return string.Compare(x, _offset, y, _offset, _len); } } private void button13_Click(object sender, EventArgs e) { ArrayList arraylist = new ArrayList(); for (int i = 0; i < listBox1.Items.Count; i++) { string temp = listBox1.Items[i].ToString(); if (temp.Length>65) { arraylist.Add(temp); } } Array.Sort(arraylist, new SubstringComparer(59, int.MaxValue)); listBox1.Items.Clear(); for (int i = 0; i < arraylist.Count; i++) listBox1.Items.Add(arraylist[i]); } } TNX for the help

modified on Saturday, December 08, 2007 10:45:32 AM

[Luc Pattyn]

Hi George, there are basically two ways (old and new): 1. if you want to sort an ArrayList in a special way, you need to create an object that implements IComparer (without < string> ) and knows how to compare two items. Its signature MUST be public int Compare(object obj1, object obj2) There is no override, by writing ": Icomparer" you promise to implement the formentioned method. And you need to cast the arguments to strings explicitly, as in: string str1=(string)obj1 2. Starting with .NET 2.0 you can also use generic collections. The code Guffa showed you is fine if you keep the strings in a generic list, that is a List< string>. In that case you inherit from IComparer< string> and your Compare method takes string arguments directly, but still there is no override involved. The generics stuff basically makes all the castings redundant. Regards,

Luc Pattyn [Forum Guidelines] [My Articles]

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[Guffa]

Oh, you are not using an array at all, but an ArrayList. That's a big difference. Then you need a comparer that handles objects: class SubstringComparer : IComparer { private int _offset, _len; public SubstringComparer(int offset, int len) { _offset = offset; _len = len; } public override int Compare(object x, object y) { return string.Compare((string)x, _offset, (string)y, _offset, _len); } } And use it like this: arraylist.Sort(new SubstringComparer(59, int.MaxValue));

Experience is the sum of all the mistakes you have done.

[electriac]

Still will not compile

    class SubstringComparer : IComparer
    {
        private int \_offset, \_len;
        public SubstringComparer(int offset, int len)
        {
            \_offset = offset; \_len = len;
        }
        public override int Compare(object x, object y)
            //-----------------------------------------------------------------------
            //        On Compare I still get no suitable method to overide
            //
            //-----------------------------------------------------------------------
        {
            return string.Compare((string)x, \_offset, (string)y, \_offset, \_len);
        }
    }

    private void button13\_Click(object sender, EventArgs e)
    {
        ArrayList arraylist = new ArrayList();
        for (int i = 0; i < listBox1.Items.Count; i++)
        {
            string temp = listBox1.Items\[i\].ToString();
            if (temp.Length>65)
            {
                    arraylist.Add(temp);
            }
        }
        
        arraylist.Sort(new SubstringComparer(59, int.MaxValue)); 
      
        listBox1.Items.Clear();
        for (int i = 0; i < arraylist.Count; i++)
            listBox1.Items.Add(arraylist\[i\]);
    }

[electriac]

Is it possible that my problem is associated with the fact that I am using .NET 3.5 and Visual 2008.

[Guffa]

Silly me... It's an interface, so you don't override the methods. Just remove the override keyword.

Experience is the sum of all the mistakes you have done.

modified on Monday, December 10, 2007 7:05:57 PM

[Luc Pattyn]

Hi George, I don't know for sure about 3.5/2008 since I haven't used them yet. but there are some problems in the code you posted, as I pointed out before. For one you should drop the "override" then choose either an ArrayList (1. in my earlier reply) or List< string> (2) and make your Compare accordingly. :)

Luc Pattyn [Forum Guidelines] [My Articles]

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Sorry for any delays in replying, I currently don't get e-mail notifications.

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[DaveyM69]

I haven't investigated to see if there are any new 'features' in this regard - but Generic Lists, IComparer and IComparable definately function as before and none of the 'normal' methods have changed in VS2008/.NET3.5 To be honest, so far I've had no problems coding exactly the same as I did with 2005 with all classes/interfaces etc.

[electriac]

Guffa Many thanks for your help and persistence sticking with me until the code was working. I have now implemented the methods you suggested in numerous programs and it has proven a valuable addition. Thanks Again

[electriac]

I have found also that all my old code could migrate without problem.