Duplicates in a Listbox 2

[rstum2005]

Im having problems removing dupes from a listbox. It seems to work well on smaller lists but for some reason on other lists it removes more than just dupes.

if(dupes==false)
{
for (int i = 0; i < listBox1.Items.Count; i++)
{
for (int j = 0; j < listBox1.Items.Count; j++)
{
if (listBox1.Items[i].ToString() == listBox1.Items[j].ToString())
{				
listBox1.Items.Remove(listBox1.Items[i].ToString());
statusBar1.Panels[0].Text ="Processing: " + i;
}
}
}

 

[earthandfire]

The item index will automatically change as you remove items.

Start from the end and work down to 0


Hope this helps.

 

[rstum2005]

I tried a few ways but it does not remove all the dupes.

if(dupes==false)
{
for (int j = 0; j < listBox1.Items.Count; j++)
{
for(int i=listBox1.Items.Count-1; i>-1; i--)
{
if(listBox1.Items[i].ToString() == listBox1.Items[i].ToString())
{				
listBox1.Items.Remove(listBox1.Items[j].ToString());
break;
}
}
				}

 

[earthandfire]

My C# is pretty useless, so I've attempted to edit your original code to show what I meant

if(dupes==false)
{
//for (int i = 0; i < listBox1.Items.Count; i++)
for (int i=listBox1.Items.Count-1; i>-1; i--)
{
//for (int j = 0; j < listBox1.Items.Count; j++)
// The following line could be one of 
for (int i=listBox1.Items.Count-1; i>-1; i--)
//for (int i=listBox1.Items.Count-1; i>0; i--)
{
if (listBox1.Items[i].ToString() == listBox1.Items[j].ToString())
{                
listBox1.Items.Remove(listBox1.Items[i].ToString());
statusBar1.Panels[0].Text ="Processing: " + i;
}
}
}

Hope this makes sense.

 

[chmohan]

an idea would be of storing the index of the dupes in an array and then removing them all with removeat in another loop

 

[earthandfire]

I'm not sure, but I think that the problem with that would be the same - because the item index would recalculate after each RemoveAt, the indices in the array would become invalid after the first removal.

 

[JurkMonkey]

Has anyone noticed that you are comparing Listbox1 to Listbox1, not listbox1 to listbox2?

 

[earthandfire]

Isn't the idea to remove duplicate values from within Listbox1

 

[JurkMonkey]

crap.

 

[earthandfire]

?

 

[chmohan]

hmm you may have to do listbox1.refresh after each item being removed or something as the count will have changed wont it when you remove an item?

 

[chmohan]

you cold remove the dups when you are loading the listbox cant you? either when u do sql query to load or when you load on the ui

 

[JurkMonkey]

string results[] = yourarrayofstrings;

ArrayList templist = new ArrayList();

for (int i = 0; i < results.Length; i++)
{
if (!templist.Contains(results)
{
templist.Add(results);
}
}

results = (string[])templist.ToArray(typeof(string));

for (int i = 0; i < results.Length; i++)
{
ListBox1.Items.Add(results);
}

 

[KarveR]

basicaly what JurkMonkey said, but fixed his freehand typos (oh the joy of devstudio) and because of youy recent post a removal of blanks and new lines:

string[] results = { "test", "test2", "test3", "test", "a", "b", "a", "\n", "c","test"," ","z"};
			
				

					ArrayList templist = new ArrayList();

				for (int i = 0; i < results.Length; i++)
				{
					if (!templist.Contains(results[i]))
					{
						templist.Add(results[i]);
					}
				}

				results = (string[])templist.ToArray(typeof(string));

				for (int i = 0; i < results.Length; i++)
				{
					if (results[i].Trim().Length > 0) 
					{
						listBox1.Items.Add(results[i]);
					}
				}

______________________________________________________________________
There's no present like the time, they say. - Henry's Cat.

 

[earthandfire]

I'm not going to attempt a C# solution however this should be easy for a C# programmer to convert:

To populate the listbox:

    'Either use this
    'For a As Integer = 0 To 100
    '  ListBox1.Items.Add(CInt(Rnd(a) * 10))
    'Next

    'or use this
    Dim results() As String = {"test", "test2", "test3", "test", "a", "b", "a", "\n", "c", "test", " ", "z"}
    For a As Integer = 0 To results.Length - 1
      ListBox1.Items.Add(results(a))
    Next

and to remove duplicates:

    Dim a As Integer
    Dim b As Integer
    Dim done As Boolean

    done = False
    a = 0
    While Not done
      For b = ListBox1.Items.Count - 1 To a + 1 Step -1
        If ListBox1.Items(a).ToString = ListBox1.Items(b).ToString Then
          ListBox1.Items.RemoveAt(b)
        End If
      Next
      a += 1
      done = a > ListBox1.Items.Count - 1
    End While

The previous two solutions (JurkMonkey and KarveR) seem to be procesing the listbox to create an array of unique values and then to essentially replace the contents of the listbox with this unique list.

My solution simply removes the duplicates. It iterates through the listbox, comparing the current value with each currently unchecked value (from back to front) removing duplicates as they are found.

JurkMonkey, I'm still confused as to the purpose and meaning of your post

JurkMonkey (Programmer) 27 Oct 05 15:10
crap.

Hope this helps.

 

[JurkMonkey]

JurkMonkey Sez: Has anyone noticed that you are comparing Listbox1 to Listbox1, not listbox1 to listbox2?

earthandfire Sez: Isn't the idea to remove duplicate values from within Listbox1

JurkMonkey Sez: Crap. Implying that I made a boo boo in my post before.

 

[earthandfire]

Sorry, I misunderstood

By the way, I spent about an hour and a half NOT writing my sample above in C#, I'd love to see a translation if you've got five minutes or so.

Thanks

 

[JurkMonkey]

So step 1, you create an array of strings:

Dim results() As String = {"test", "test2", "test3", "test", "a", "b", "a", "\n", "c", "test", " ", "z"}
For a As Integer = 0 To results.Length - 1
ListBox1.Items.Add(results(a))
Next

C# is essentially the same, only you define the type of variable first.

Dim results() becomes string[] results and you set it:

string[] results = new string{"test", "test2", "test3", "test", "a", "b", "a", "\n", "c", "test", " ", "z"}


Step 2 was to declare some local variables used to control the loop. You will notice that you used 3 variables (a, b, and done) - a is first set to 0, and used as an index in the listbox. b is set to the total number of listbox items (-1 because a listbox index starts at 0) and decrements by 1 every time.

So what you're actually doing is looping through the entire list, 1 item at a time (a) and checking if it is equal to the item indexed by (b). If it is the same then you remove the item indexed by (b).

In step 3, you decide if the index of a is greater than the total number of items in the listbox.



I hope you're not lost so far.


I wrote the code using 3 examples.

1. Converting what you are using to C#
2. Cleaning up the example you provided using C#
3. The arraylist method which actually creates the correct list of items.


Create a project called "Stuff" and copy this code into it.

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace Stuff
{
	/// <summary>
	/// Summary description for Form1.
	/// </summary>
	public class Form1 : System.Windows.Forms.Form
	{
		private System.Windows.Forms.ListBox listBox1;
		private System.Windows.Forms.ListBox listBox2;
		private System.Windows.Forms.Button button1;
		private System.Windows.Forms.Button button2;
		private System.Windows.Forms.Button button3;
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.Container components = null;

		public Form1()
		{
			//
			// Required for Windows Form Designer support
			//
			InitializeComponent();

			//
			// TODO: Add any constructor code after InitializeComponent call
			//
		}

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
			this.listBox1 = new System.Windows.Forms.ListBox();
			this.listBox2 = new System.Windows.Forms.ListBox();
			this.button1 = new System.Windows.Forms.Button();
			this.button2 = new System.Windows.Forms.Button();
			this.button3 = new System.Windows.Forms.Button();
			this.SuspendLayout();
			// 
			// listBox1
			// 
			this.listBox1.Items.AddRange(new object[] {
														  "a",
														  "b",
														  "c",
														  "a",
														  "c",
														  "d",
														  "e",
														  "f",
														  "d",
														  "f",
														  "g",
														  "h",
														  "i",
														  "j",
														  "k"});
			this.listBox1.Location = new System.Drawing.Point(8, 8);
			this.listBox1.Name = "listBox1";
			this.listBox1.Size = new System.Drawing.Size(152, 212);
			this.listBox1.TabIndex = 0;
			// 
			// listBox2
			// 
			this.listBox2.Location = new System.Drawing.Point(296, 8);
			this.listBox2.Name = "listBox2";
			this.listBox2.Size = new System.Drawing.Size(144, 212);
			this.listBox2.TabIndex = 1;
			// 
			// button1
			// 
			this.button1.Location = new System.Drawing.Point(184, 16);
			this.button1.Name = "button1";
			this.button1.TabIndex = 2;
			this.button1.Text = "Proposed";
			this.button1.Click += new System.EventHandler(this.button1_Click);
			// 
			// button2
			// 
			this.button2.Location = new System.Drawing.Point(184, 56);
			this.button2.Name = "button2";
			this.button2.TabIndex = 3;
			this.button2.Text = "Cleaned";
			this.button2.Click += new System.EventHandler(this.button2_Click);
			// 
			// button3
			// 
			this.button3.Location = new System.Drawing.Point(184, 104);
			this.button3.Name = "button3";
			this.button3.TabIndex = 4;
			this.button3.Text = "ArrayList";
			this.button3.Click += new System.EventHandler(this.button3_Click);
			// 
			// Form1
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(744, 590);
			this.Controls.Add(this.button3);
			this.Controls.Add(this.button2);
			this.Controls.Add(this.button1);
			this.Controls.Add(this.listBox2);
			this.Controls.Add(this.listBox1);
			this.Name = "Form1";
			this.Text = "Form1";
			this.ResumeLayout(false);

		}
		#endregion

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
		}

		private void button1_Click(object sender, System.EventArgs e)
		{
			listBox2.Items.Clear(); //Clear the differences box
			//The proposed method
			//I have preset the items in the listbox

			int a = 0;
			bool done = false;

			while (done == false) //or while (!done)
			{
				for (int b = listBox1.Items.Count - 1; b > a; b--) 
				{
					if (listBox1.Items[a].ToString() == listBox1.Items[b].ToString())
					{
						listBox2.Items.Add(listBox1.Items[b]); //I added this to show which items have been removed
						listBox1.Items.RemoveAt(b);
					}
				}

				a+=1;
				done = (a > listBox1.Items.Count - 1);
			}
		}

		private void button2_Click(object sender, System.EventArgs e)
		{
			listBox2.Items.Clear(); //Clear the differences box
			//This is a slightly cleaned up version of the above code.
			//I have preset the items in the listbox

			for (int a = 0; a <= listBox1.Items.Count; a++)
			{
				for (int b = listBox1.Items.Count - 1; b > a; b--) 
				{
					if (listBox1.Items[a].ToString() == listBox1.Items[b].ToString())
					{
						listBox2.Items.Add(listBox1.Items[b]); //I added this to show which items have been removed
						listBox1.Items.RemoveAt(b);
					}
				}
			}
		}

		private void button3_Click(object sender, System.EventArgs e)
		{
			listBox2.Items.Clear(); //Clear the differences box
			//Using an arraylist, I create a new list of correct items - no dupilcates
			//I have preset the items in the listbox

			ArrayList templist = new ArrayList();

			for (int i = 0; i < listBox1.Items.Count; i++)
			{
				if (!templist.Contains(listBox1.Items[i]))
				{
					templist.Add(listBox1.Items[i]);
				}
			}

			//results is a list of the items with the duplicate values already removed.
			string[] results = (string[])templist.ToArray(typeof(string));

			for (int i = 0; i < results.Length; i++)
			{
				if (results[i].Trim().Length > 0) 
				{
					listBox2.Items.Add(results[i]);
				}
			}

		}
	}
}

 

[earthandfire]

Thanks for that.

In VB we can't duplicate:

for (int b = listBox1.Items.Count - 1; b > a; b--)

hence the need for the while loop.


I seem to remember some time ago you demonstrated this technique to me - and that is what I was trying (unsuccessfully) to do before I gave up and wrote it in VB.

I haven't tested your code yet, its 03:48 UK time and I've had enough programming for the day - but I think a star is definitely called for.

Thanks again

 

[rstum2005]

Hey Thanks All, This really helped me out.

Thanks again.