Remove duplicates from arraylist of objects

Question

I'm trying to remove duplicates of one arraylist filled with the objects "DataPerLabel".

DataPerLabel contains the following methods: getLabelname(), getLabelAdress() and getDataType().

Some background information:

The values labelname, labelAdress and dataType can be set as 1 object in an arraylist named allData by a submit button. When submit is pressed for the 2nd time i want to delete that object of the arraylist.

Picture:

Some of the code i've tried:

if (submitButtonClicked == true) {
  if (MessageBox.Show("This is item is already set. Do you want to delete?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes) {
    foreach(DataPerLabel item in allData) {
        if (item.getDataType().Equals(dataType) && item.getLabelAdress().Equals(adress) && item.getLabelName().Equals(label)) {
          allData.Remove(item);
        } else {

        }
    }
  } else {
    //no
  }

}

With this code i'm getting the following error: An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll.

Additional error information: The collection has been changed.

Answer 1

You are trying to iterate in allData list and you are also trying to modify the same list. You can keep removing datas in an other list(eg: removeItems) and then you can remove items. I mean :

   if (submitButtonClicked == true) {
      if (MessageBox.Show("This is item is already set. Do you want to delete?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes) {
List<DataPerLabel> removeItems = new List<DataPerLabel>();
        foreach(DataPerLabel item in allData) {
            if (item.getDataType().Equals(dataType) && item.getLabelAdress().Equals(adress) && item.getLabelName().Equals(label)) {
              removeItems.Add(item);
            } else {

            }
        }
      } else {
        //no
      }

    foreach(DataPerLabel removeItem in removeItems ){
        allData.Remove(removeItem);
      }

}

Answer 2

        //Here is just an example of list of array 
       List<object> obj = new List<object>();
        obj.Add(5);
        obj.Add(4);
        obj.Add("we");
        obj.Add(5);
        List<object> objTodelete = new List<object>();

        foreach (var item in obj)
        {
            int count = obj.Count(a => a.ToString() == item.ToString());
            //for finding the dublicate occurence
            if (count > 1)
            {
                //for removing that dublicated occurence.
                object Dublicate = obj.Find(m => m.ToString() == item.ToString());
                if (!objTodelete.Contains(Dublicate))
                {
                    objTodelete.Add(Dublicate); 
                }
            }
        }
        foreach (var itemDublicate in objTodelete)
        {
            obj.Remove(itemDublicate);
        }

Answer 3

As OnurBulbul said you get an exception due trying to modify the list you are iterating through. There are a lot of different solution could be. My suggestion is to use LINQ:

var sortedList = from item in allData
                 where !(item.getDataType().Equals(dataType) && item.getLabelAdress().Equals(adress) && item.getLabelName().Equals(label))
                 select item

It will create a new arrayList for you with all sorted out data