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: Example

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.

Possible duplicate of linq & distinct, implementing the equals & gethashcode — pix
– pix, Commented Sep 20, 2017 at 6:55

OnurBulbul · Accepted Answer · 2017-09-20 07:02:17Z

3

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);
      }

}

answered Sep 20, 2017 at 7:02

OnurBulbul

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2 Comments

Pawelotti Over a year ago

It would be a bit simplier without second foreach but with: allData.RemoveRange(removeItems);

NielsSchutte Over a year ago

I've used this method, works for me. Thank you all of you!

OlegI · Accepted Answer · 2017-09-20 07:24:39Z

0

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

edited Sep 20, 2017 at 7:24

answered Sep 20, 2017 at 7:12

OlegI

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Comments

Pradeep Kumar · Accepted Answer · 2017-09-20 08:13:02Z

0

        //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);
        }

edited Sep 20, 2017 at 8:13

answered Sep 20, 2017 at 7:11

Pradeep Kumar

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5 Comments

Pradeep Kumar Over a year ago

First make a loop for occurrence and then find the index of the occurence and then remove.

nbokmans Over a year ago

Why first check if there is any object with Count and then query again if so? You could just check if var item = obj.FirstOrDefault(a => a.ToString() == item.ToString());, after which you can just check if (item != null) { and obj.Remove(item);.

OlegI Over a year ago

It will cause the same exception as author's 'System.InvalidOperationException'. It is not possible to modify object during iterating through it

NielsSchutte Over a year ago

Thanks for ur answer, got it now.

Pradeep Kumar Over a year ago

yes u r right! For first loop add the duplicate item to another list and the remove that another list from main list. or you can use for loop instead of Foreach. This will not throw 'System.InvalidOperationException'.

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