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C# dictionary value is updating automatically

In my recent project im trying to make a dictionary with key as a string and value as List of string(List) and adding value in dictionary using for loop ,
but the problem is that after first iteration when I Update the List for second iteration it is automatically changing in the first key value pair.
for example in first iteration it is saving key as apple and value as list {cucumber,chilli,tomato,apple} its fine but after first iteration when i update list to {cucumber,chilli,tomato,apple,mango} and saving it to second key mango it is also updating the first value to {cucumber,chilli,tomato,apple,mango}.
var mylist = new List<string>()
{
"cucumber",
"chilli",
"tomato"
};
var yourlist = new List<string>()
{
"apple",
"mango",
"banana"
};
var dict = new Dictionary<string, List<string>>();
foreach (var i in yourlist)
{
mylist.Add(i);
dict.Add(i,mylist);
}
foreach(var d in dict.Keys)
{
foreach(var l in dict[d])
{
Console.WriteLine(l);
}
}

The dictionary entries' Value properties are always the same list, so anything you do to one, ends up showing in all of them (because there is only one)
Take a look at the code below; if you understand why a and b here both show the same change, then you should understand that your dictionary scenario is essentially the same
var list = new List<string>(){ "hello", "world" };
var a = list;
var b = list;
a.Add("there");
Console.Write(b.Count); //shows 3
If you don't understand why a, b and list above all refer to the same list, then drop a comment and I'll add some more explanation
As to what you should do about your "issue", it's not entirely clear to me what you're hoping to do but if you made sure that each key in the dictionary associated with a new list rather than the same one, then changes to one key's list would not show in other keys' lists:
dict.Add(i, new List<string>(mylist));
This makes a new list per key, and initializes the new list with the items present in mylist at the time (my list grows each pass of the loop)

Compare Sharepoint List with C#

I am trying to compare two Sharepoint lists. I am using a C# program to add, update, and delete items, based on its ID. If the ID doesnt exist in List1, when the program is ran, I want to delete the IDs from List2. I was wondering how can I delete those items without specifying a specific number in the GetItemById function? Like in this example
using(ClientContext context = new ClientContext(siteUrl)) {
//Retrieve list items from list 1 here code here
using(ClientContext target = new ClientContext(siteUrl2)) {
foreach(ListItem oListItem2 in collListItem2) {
int exists = 0;
foreach(ListItem oListItem in collListItem) {
if (oListItem2["ID"] == oListItem["ID"]) {
exists++;
}
}
if (exists == 0) {
ListItem DeleteItem = list2.GetItemById();
DeleteItem.DeleteObject();
target.ExecuteQuery();
}
return;
}
}
}

To delete the items from the second list not in the first, just get all of the items from the first list, and filter the items in the second list based on those ids. Note you can use a hash based lookup to greatly improve performance over a linear search:
var idsFromFirstList = new HashSet<int>(
collListItem.AsEnumerable()
.Select(item => item.Id));
var itemsToDelete = collListItem2.AsEnumerable()
.Where(item => !idsFromFirstList.Contains(item.Id);
foreach(var item in itemsToDelete)
item.DeleteObject();
target.ExecuteQuery();
Note that you can basically do the exact opposite to find the items to add (create a hashset of the IDs of the items in the target into a set, find all items in the first no tin there, and then add all of those items).
To find items that match you can use a Dictionary<int, ListItem> by putting either set of items into a dictionary, with the ID as the key, and going through the other set, finding the matches. If you are going to do that, you can re-use that dictionary to check for one of the other two conditions as well, to save you one data structure:
var firstSiteItemLookup = collListItem.AsEnumerable()
.ToDictionary(item => item.Id, item => item);
foreach(var item in collListItem2)
{
ListItem match;
if(firstSiteItemLookup.TryGetValue(item.Id, out match))
UpdateItemToMatch(item, match);
else
item.DeleteObject();
}
target.ExecuteQuery();

Can you use the same code to check if an ID in collListItem has been modified then update the same ID in collListItem2? #Servy

Why am I getting ArgumentOutOfRangeException in Lists?

I am using List of Lists in my project. When i run program i get ArgumentOutOfRangeException. But there is no range specified in list.
I declared list like this:
public static List<List<string>> list = new List<List<string>>();
Now i want to add my name in the first "list" which is in the List of lists.
list[0].Add("Hussam"); //Here i get ArgumentOutOfRange Exception.
What should I do now?

But there is no range specified in list
No, there's an index specified (as an argument), and that's what's out of range. Look at your code:
list[0].Add("Hussam");
That's trying to use the first list in list - but is list is empty, there is no first element. The range of valid arguments to the indexer is empty, basically.
So first you want:
list.Add(new List<string>());
Now list[0] will correctly refer to your empty List<string>, so you can add "Hussam" to it.

You want to add an item to the first item in an empty list... That isn't going to work. First, add the list inside the other list:
public static List<List<string>> list = new List<List<string>>();
List<string> innerList = new List<string>();
list.Add(innerList);
innerList.Add("Hussam");

Why are you creating a list of a list? Wouldn't List suffice? What is happening here is the inner list is not being initialized.
list.Add(new List<string>());
list[0].Add("Jimmy");

In this case ocurred an exception because you tried acess an index which not exists, then you must add an inner initial list, which could be done follows:
list.Add(new new List<string>());
Or, if you want add an first name directly:
list.Add(new new List<string>(){"Hussam"});

Ok so first, you have to understand that the "index" only comes after the value has been declared. Lists behave different. They are not like arrays. You get the index in which you want to store the item and when you do that, you use the code array[index] = value;.
But in a List, to give a value to a completely new item, you use the method Add(value).
So here's a reminder: Systems.Collections.Generic.List<> has nothing to do with array[ ]s

You cannot access list[0] as there is no item at index 0. The list is empty.
You need to add a new List like this:
list.Add(new List<string> { "Hussam" });
or, assign a list to index 0 and then add to it as per your posted code:
list.Add(new List<string>());
list[0].Add("Hussam");
If you don't always know if the list will be be empty or not you can use FirstOrDefault (a LINQ method) to check if there is any entry at index 0 and assign one if not, otherwise use the existing inner list:
var innerList = list.FirstOrDefault();
if (innerList == null)
{
innerList = new List<string>();
list.Add(innerList);
}
innerList.Add("Hussam");

The problem is, your nested list hasn't been initialized, with anything.
So, calling the first item of the nested list is correctly telling you there is nothing in it.
To verify:
int superlistCounter = 1;
int sublistCounter = 1;
foreach(var sublist in list)
{
Console.WriteLine("Now in List #" + superlistCounter);
foreach(var item in sublist)
{
Console.WriteLine("List item #" + sublistCounter + ": " + item)
}
}
The output will be:
Now in List #1
It sounds like you're expecting:
Now in List #1
List Item #1: Hussam
To fix this, simply initialize your list!
public static List<List<string>> list = new List<List<string>>();
// ...
List<string> subList1 = new List<string>();
list.Add(subList1);
subList1.Add("Hussam");

Compare values in Dictionary with Another List Items

I have a problem here. I have implemented a dictionary MASTERDATALIST and a list DEPARTMENTLIST containing s specific set of items.
What I need is to compare the values of each key in MASTERDATALIST with the items of DEPARTMENTLIST.
If they are not equal, then that key should be added to another list "FAILEDLIST"
Any help would be appreciated.
Thanks!

I'm assuming that what you mean by If they are not equal is If the key is not found in the list.
What you need to do is:
loop through the items in MasterDataList
loop through the values for each item in the dictionary
check if DepartmentList contains this item
if not, add the item to FailedList
MasterDataList.Add("key1", new List<string>() { "list1_item1", "list1_item2" });
MasterDataList.Add("key2", new List<string>() { "list2_item1", "list2_item2" });
MasterDataList.Add("key3", new List<string>() { "list3_item1", "list3_item2" });
DepartmentList.Add("list1_item1");
DepartmentList.Add("list1_item2");
DepartmentList.Add("list2_item1");
DepartmentList.Add("list2_item2");
foreach (KeyValuePair<string, List<string>> item in MasterDataList)
{
foreach (var listItem in item.Value)
{
if (!DepartmentList.Contains(listItem))
FailedList.Add(listItem);
}
}
foreach (var item in FailedList)
{
Console.WriteLine(item);
}
Console.ReadLine();

Iterating over a growing dictionary

I am working with C# and I have a dictionary called intervalRecordsPerObject of type Dictionary<string, List<TimeInterval>>. I need to iterate through the dictionary. The problem is: everytime I iterate through the dictionary, more KeyValuePairs may get added to it. As the dictionary grows, I need to keep iterating over the new entries too.
Firstly, I did this: A simple foreach loop that gave me an InvalidOperationException saying
Collection was modified; enumeration operation may not execute.
I know I cannot iterate over the Dictionary this way if it keeps changing as C# converts it with ToList() before foreach loop.
I know I can copy the keys to a temporary array, iterate over the dictionary using simple for loop and Count and whenever a new entry is added to the dictionary, add the corresponding key to the array too. Now, the problem is a simple array cannot grow dynamically and I don't know beforehand what the required size could be.
To move ahead, I thought I'd do this:
List<string> keyList = new List<string>(intervalRecordsPerObject.Count);
intervalRecordsPerObject.Keys.CopyTo(keyList.ToArray(), 0);
I cannot do this either. keyList is currently empty and therefore keyList.toArray() returns an array of length 0 which gives me an ArgumentException saying
Destination array is not long enough to copy all the items in the
collection. Check array index and length.
I am stuck! Any idea what more can I try? Thanks for any help.
Addition 1:
The dictionary stores the time intervals for which a particular object is present. Key is the ID of the object. New entries may get added in every iteration (worst case) or may not get added even once. Whether or not entries are added is decided by a few conditions (whether the object overlaps with some other intervals, etc.). This triggers a change in the ID and the corresponding interval list which is then added as a new entry to the dictionary.

Something like this:
List<string> keys = dict.Keys.ToList();
for (int i = 0; i < keys.Count; i++)
{
var key = keys[i];
List<TimeInterval> value;
if (!dict.TryGetValue(key, out value))
{
continue;
}
dict.Add("NewKey", yourValue);
keys.Add("NewKey");
}
The trick here is that you enumerate the List<T> by index! In this way, even if you add new elements, the for (...) will "catch" them.
Other possible solution, by using a temporary Dictionary<,>:
// The main dictionary
var dict = new Dictionary<string, List<TimeInterval>>();
// The temporary dictionary where new keys are added
var next = new Dictionary<string, List<TimeInterval>>();
// current will contain dict or the various instances of next
// (multiple new Dictionary<string, List<TimeInterval>>(); can
// be created)
var current = dict;
while (true)
{
foreach (var kv in current)
{
// if necessary
List<TimeInterval> value = null;
// We add items only to next, that will be processed
// in the next while (true) cycle
next.Add("NewKey", value);
}
if (next.Count == 0)
{
// Nothing was added in this cycle, we have finished
break;
}
foreach (var kv in next)
{
dict.Add(kv.Key, kv.Value);
}
current = next;
next = new Dictionary<string, List<TimeInterval>>();
}

You can access the Keys by positions rather than by content and use a normal For loop (allowing additions/removals without any restriction).
for (int i = 0; i < dict.Keys.Count; i++)
{
string curKey = dict.Keys.ElementAt(i);
TimeInterval curVal = dict.Values.ElementAt(i);
//TimeInterval curVal = dict[curKey];
//Can add or remove entries
}