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How to remove duplicates from object list based on that object property in c#

I've got a problem with removing duplicates at runtime from my list of object.
I would like to remove duplicates from my list of object and then set counter=counter+1 of base object.
public class MyObject
{
MyObject(string name)
{
this.counter = 0;
this.name = name;
}
public string name;
public int counter;
}
List<MyObject> objects_list = new List<MyObject>();
objects_list.Add(new MyObject("john"));
objects_list.Add(new MyObject("anna"));
objects_list.Add(new MyObject("john"));
foreach (MyObject my_object in objects_list)
{
foreach (MyObject my_second_object in objects_list)
{
if (my_object.name == my_second_object.name)
{
my_object.counter = my_object.counter + 1;
objects_list.remove(my_second_object);
}
}
}
It return an error, because objects_list is modified at runtime. How can I get this working?

With a help of Linq GroupBy we can combine duplicates in a single group and process it (i.e. return an item which represents all the duplicates):
List<MyObject> objects_list = ...
objects_list = objects_list
.GroupBy(item => item.name)
.Select(group => { // given a group of duplicates we
var item = group.First(); // - take the 1st item
item.counter = group.Sum(g => g.counter); // - update its counter
return item; // - and return it instead of group
})
.ToList();

The other answer seem to be correct, though I think it will do scan of the whole list twice, depending on your requirement this might or might not be good enough. Here is how you can do it in one go:
var dictionary = new Dictionary<string, MyObject>();
foreach(var obj in objects_list)
{
if(!dictionary.ContainsKey(obj.name)
{
dictionary[obj.name] = obj;
obj.counter++;
}
else
{
dictionary[obj.name].counter++;
}
}
Then dictionary.Values will contain your collection

C# Remove line of data from List

Here is my List declaration:
public List<CharactersOnline> charactersOnline = new List<CharactersOnline>();
public class CharactersOnline
{
public int connectionId;
public int characterId;
public string characterName;
}
Here is how i add lines into this list:
charactersOnline.Add(new CharactersOnline() { connectionId = cnnId, characterId = charId, characterName = name });
Here is how i think i can remove one line by just poiting one of the parameters:
private void CharacterLogout(int charId)
{
charactersOnline.Remove(new CharactersOnline() { characterId = charId });
}
Can i remove all the data on the line of the list by just pointing only one of the parameters or this is just going to delete the data for characterId only ?
I need to know how can i delete the whole line of this list.

One way to do that is to find it and then remove it:
var charactersOnline = new List<CharactersOnline>();
var target = charactersOnline.SingleOrDefault(x => x.characterId == 1);
charactersOnline.Remove(target);
So your method will be like this:
private void CharacterLogout(int charId)
{
var target = charactersOnline.SingleOrDefault(x => x.characterId == charId);
charactersOnline.Remove(target);
}

Another approach in more functional way.
private void CharacterLogout(int charId)
{
charactersOnline = charactersOnline.Where(line => line.characterId != charId)
.ToList();
}
Notice, that approach above will remove all lines with given charId value.
Your approach will not work because Remove method will search for element with same reference as given item to remove.
The line new CharactersOnline() { characterId = charId } will create new instance of object which reference not exists in the list.
So for removing correct item you should find it first.
var indexesToRemove =
charactersOnline.Select((line, index) => (Id: line.characterId, Index: index))
.Where(item => item.Id == charId)
.Select(item => item.Index);
foreach (var index in indexesToRemove)
{
charactersOnline.RemoveAt(index);
}

Use this code to remove item from List based on condition
charactersOnline.Remove(charactersOnline.Single(s => s.characterId = charId) );

Taking a set of items from a list and to perform some operation based on need

I have a list of items in a list. From that list I need to take the first 1000 items and need to submit the package and then again I need to take another 1000 and need to submit a package. If the list is not having 1000 I need to submit the package with all the items. for that I wrote the following code which is returning an error as collection modified.
List<SyncQueue> tempMassiveSyncQueue=massiveSyncQueue;
while (tempMassiveSyncQueue.Count != 0)
{
int MassivePackageFileCount =Convert.ToInt32(ConfigurationManager.AppSettings["MassivePackageFileLimit"]);
massiveSyncQueues = tempMassiveSyncQueue;
List<SyncQueue> tempMassivePackageSyncQueue=new List<SyncQueue>();
if (massiveSyncQueues.Count > 1000
{
var massivePackageSyncQueue = (massiveSyncQueues.Take(1000)).ToList<SyncQueue>();
tempMassivePackageSyncQueue = massivePackageSyncQueue;
SubmitPackage(massivePackageSyncQueue);
}
if (tempMassivePackageSyncQueue.Count != 0)
{
foreach (var massivesynq in tempMassiveSyncQueue)
{
foreach (var deleteId in tempMassivePackageSyncQueue.Where(id => id.SyncQueueId == massivesynq.SyncQueueId))
{
tempMassiveSyncQueue.Remove(massivesynq);
}
}
}
else
{
SubmitPackage(massiveSyncQueues);
}
massiveSyncQueues = null;
}
Can any one help on this?

Incorporate Skip into your logic
int loopCount = 0;
While(true)
{
var ListToProcess = massiveSyncQueue.Skip(loopCount*1000).Take(1000);
SubmitPackage(ListToProcess);
if(ListToProcess.Count < 1000) // We know there are no more in the list massive list.
{
break;
}
loopCnt++;
}

Your problem is that you are adjusting the collection on which the bounds of the foreach construct are set.
Try using ToList() on the collection you are looping through, as this creates a new List in memory:
foreach (var massivesynq in tempMassiveSyncQueue.ToList())
{
foreach (var deleteId in tempMassivePackageSyncQueue.Where(id => id.SyncQueueId == massivesynq.SyncQueueId).ToList())
{
tempMassiveSyncQueue.Remove(massivesynq);
}
}

In line 1 you set tempMassiveSyncQueue = massiveSyncQueue, yet within the while loop you set massiveSyncQueue = tempMassiveSync.
The collection modified error usually occurs when you modify the collection you are looping through. Which is why you need to first create a copy of the collection which is INDEPENDANT to the original collection and loop through that.
Before the while loop you need to add all items in massiveSyncQueue to tempMassiveSyncQueue. You then need to loop through the temp list with your code. In the second loop, you are removing items from the list you are looping through. I assume you meant to remove the items from massiveSyncQueue and not the temp list.
Try the following:
List<SyncQueue> tempMassiveSyncQueue = new List<SyncQueue>();
foreach(var item in massiveSyncQueue)
{
tempMassiveSyncQueue.Add(item);
}
while (tempMassiveSyncQueue.Count != 0)
{
int MassivePackageFileCount = Convert.ToInt32(ConfigurationManager.AppSettings["MassivePackageFileLimit"]);
List<SyncQueue> tempMassivePackageSyncQueue=new List<SyncQueue>();
if (massiveSyncQueues.Count > 1000
{
var massivePackageSyncQueue = (massiveSyncQueues.Take(1000)).ToList<SyncQueue>();
tempMassivePackageSyncQueue = massivePackageSyncQueue;
SubmitPackage(massivePackageSyncQueue);
}
if (tempMassivePackageSyncQueue.Count != 0)
{
foreach (var massivesynq in massiveSyncQueue)
{
foreach (var deleteId in tempMassivePackageSyncQueue.Where(id => id.SyncQueueId == massivesynq.SyncQueueId))
{
massiveSyncQueue.Remove(massivesynq);
}
}
}
else
{
SubmitPackage(massiveSyncQueues);
}
massiveSyncQueues = null;
}

Try this
int count=1;
while(tempMassivePackageSyncQueue.Count>1000)
{
var massivePackageSyncQueue = (massiveSyncQueues.skip(count*1000).Take(1000)).ToList<SyncQueue>();
tempMassivePackageSyncQueue = massivePackageSyncQueue;
SubmitPackage(massivePackageSyncQueue);
count++;
}
var massivePackageSyncQueue = (massiveSyncQueues.skip(count*1000).Take()).ToList<SyncQueue>();
tempMassivePackageSyncQueue = massivePackageSyncQueue;
SubmitPackage(massivePackageSyncQueue);

compare List<string> and List<T>

I'm using C# and framework 4.0.
I have a list of type string and another list of type class T;
How can I compare List with a List and save the difference?
private void simpleButton_Compare_Click(object sender, EventArgs e)
{
try
{
bool Is_Egal = true;
int i = 0;
foreach (string Od_Scan in Ordre_Scan)
{
if (!Outils.Get_Ordre_Donne()[i].NoOrdre.Contains(Od_Scan) && !String.IsNullOrWhiteSpace(Od_Scan))
{
Is_Egal = false;
Temp_Od_Scan.Add(Od_Scan);
}
i++;
}
foreach (Pers_Compare Od_Done in Outils.Get_Ordre_Donne())
{
if (!Ordre_Scan.Contains(Od_Done.NoOrdre) && !String.IsNullOrWhiteSpace(Od_Done.NoOrdre))
{
Is_Egal = false;
Temp_Od_Donne.Add(Od_Done);
}
else
{
Temp_Od_Donne_Egal.Add(Od_Done);
}
}
if (Is_Egal)
{
MessageBox.Show("égalité");
}
else
{
MessageBox.Show("PAS égalité");
}
}
catch (Exception excThrown)
{
MessageBox.Show(excThrown.Message);
}
}
and the data :
List<string> Ordre_Scan= new List<string> { "azer","qsdf"};
Pers_Compare obj = new Pers_Compare();
obj.Nolv = 1;
obj.Noordre = "qsdf"
Pers_Compare obj2 = new Pers_Compare();
obj2.Nolv = 1;
obj2.Noordre = "wxcv"
List<Pers_Compare> Ordre_Donne = new List<Pers_Compare>();
Ordre_Donne.add(obj);
Ordre_Donne.add(obj2);
And I want to save the data in Ordre_Donne but not in Od_Scan and vice versa.
foreach (string Od_Scan in Temp_Od_Scan)
{
all item that not found in List A
--> wxcv
}
foreach (var Od_Done in Temp_Od_Donne)
{
all item that not found in List B
--> azer
}

The answer given for a slightly different question (comparing a List with another List) seems to me to be a good solution for your issue, they address multiple issues to do with comparisons of lists.
EDIT: However you should be more specific with your requirements i.e. what exactly is a 'difference', e.g. is {1,1,2} and {1,2} the same?
Here is the answer given the most votes... (included here just encase it gets removed for some reason (as per Bob' suggestion))
"
DESCRIPTION:
I need to check that they both have the same elements, regardless of their position within the list. Each MyType object may appear multiple times on a list. Is there a built-in function that checks this? What if I guarantee that each element appears only once in a list?
EDIT: Guys thanks for the answers but I forgot to add something, the number of occurrences of each element should be the same on both lists.
ANSWER:
If you want them to be really equal (i.e. the same items and the same number of each item), I think that the simplest solution is to sort before comparing:
Enumerable.SequenceEqual(list1.OrderBy(t => t), list2.OrderBy(t => t))
Edit:
Here is a solution that performs a bit better (about ten times faster), and only requires IEquatable, not IComparable:
public static bool ScrambledEquals<T>(IEnumerable<T> list1, IEnumerable<T> list2) {
var cnt = new Dictionary<T, int>();
foreach (T s in list1) {
if (cnt.ContainsKey(s)) {
cnt[s]++;
} else {
cnt.Add(s, 1);
}
}
foreach (T s in list2) {
if (cnt.ContainsKey(s)) {
cnt[s]--;
} else {
return false;
}
}
return cnt.Values.All(c => c == 0);
}
Edit 2:
To handle any data type as key (for example nullable types as Frank Tzanabetis pointed out), you can make a version that takes a comparer for the dictionary:
public static bool ScrambledEquals<T>(IEnumerable<T> list1, IEnumerable<T> list2, IEqualityComparer<T> comparer) {
var cnt = new Dictionary<T, int>(comparer);
...
"

var list1 = Ordre_Donne.Where(o => !Ordre_Scan.Any(s => s == o.Noordre));
var list2 = Ordre_Scan.Where(s => !Ordre_Donne.Any(o => o.Noordre == s));

You can either implement IComparable on your Pers_Compare class, which will look something like:
public int CompareTo(string other)
{
return this.Noordre.CompareTo(other);
}
Or, if you don't have control of the data structure, you could do something like
var Temp_Od_Donne = from od in Ordre_Donne
where !Ordre_Scan.Contains(od.Noordre)
select od;
var Temp_Od_Scan = from os in Ordre_Scan
where !Ordre_Donne.Select(od => od.Noordre).Contains(os)
select os;

Check if collection is empty or not

public ActionResult Create(FormCollection collection, FormCollection formValue)
{
try
{
Project project = new Project();
TryUpdateModel(project, _updateableFields);
var devices = collection["devices"];
string[] arr1 = ((string)devices).Split(',');
int[] arr2 = Array.ConvertAll(arr1, s => int.Parse(s));
project.User = SessionVariables.AuthenticatedUser;
var time = formValue["Date"];
project.Date = time;
project.SaveAndFlush();
foreach (int i in arr2)
{
Device d = Device.Find(i);
d.Projects.Add(project);
d.SaveAndFlush();
}
return RedirectToAction("Index");
}
catch (Exception e)
{
return View(e);
}
}
I want to wrap the foreach in a if statement which checks if
var devices = collection["devices"];
is empty or not. If its empty the for each should not be executed. For the record, collection["devices"] is a collection of checkbox values from a form.

You can use the Count field to check if the collection is empty or not
so you will end up with something like this :
if(devices.Count > 0)
{
//foreach loop
}

You can use the method Any to know if a collection as any element.
if (devices.Any())
{
//devices is not empty
}

You do not need to check if the collection is empty, if it is empty the code inside the ForEach will not be executed, see my example below.
using System;
using System.Collections.Generic;
namespace Test
{
class Program
{
static void Main(string[] args)
{
List<string> emptyList = new List<string>();
foreach (string item in emptyList)
{
Console.WriteLine("This will not be printed");
}
List<string> list = new List<string>();
list.Add("item 1");
list.Add("item 2");
foreach (string item in list)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}

Your code, as it stands, won't work, as you say that collection["devices"] is a collection of checkbox values, and yet you're casting it to a string. Do you mean collection is the checkbox values? What is the exact type of collection?
Any object that implements ICollection or ICollection<T> can be checked whether it's empty or not by checking if the Count property is greater than zero.

How about checking the array length
if (arr2.length > 0)
{
foreach (int i in arr2)
{
Device d = Device.Find(i);
d.Projects.Add(project);
d.SaveAndFlush();
}
}

This worked for me in Dot Net Core but only for IEnumerable of Models not Entities
(I got a bit of help from AutoMapper)
Cast it as a List then check the Capacity
IEnumerable<vwPOD_Master> podMasters = _podRepository.GetNewPods(PartNumber);
IEnumerable<NewPODsDTO> podList = Mapper.Map<IEnumerable<NewPODsDTO>>(podMasters);
if (((List<NewPODsDTO>)podList).Capacity == 0) {
return NotFound();
}