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C# - Duplicates in List of string Lists instead of proper values

Im reading from xml file using foreach (as in below) and writing found info into a List, which then is later added to a list of lists. My problem is that the moment foreach loop is trying to add another element to my lists of lists it somehow erases the content of previous elements of the list and instead adds x of the same. E.g. first loop is ok, on the second loop it erases the first element and adds 2 of the same, on the 3rd loop it adds 3 same lists etc.
It might be a simple problem but i really cannot think of a solution to at the moment.
Code:
static List<List<string>> AddPapers(XmlNodeList nodelist)
{
var papers = new List<List<string>>();
var paper = new List<string>();
foreach (XmlNode node in nodelist)
{
paper.Clear();
for (int i = 0; i < node.ChildNodes.Count; i++)
{
paper.Add(node.ChildNodes[i].InnerText);
}
papers.Add(paper);
}
return papers;
}
More info: This is sort of a simplified version without all the fancy stuff id do with the xml but nevertheless, the problem is the same.
The paper list is good everytime i check so the problem should be with adding to papers. I honestly have no idea why or even how can it erase the contents of papers and add same values on its own.

The problem is that you're only calling paper.Clear, which clears the list that you just added, but then you re-populate it with new items and add it again.
Instead, you should create a new instance of the list on each iteration, so you're not always modifying the same list over and over again (remember a List<T> is a reference type, so you're only adding a reference to the list).
For example:
static List<List<string>> AddPapers(XmlNodeList nodelist)
{
var papers = new List<List<string>>();
foreach (XmlNode node in nodelist)
{
// Create a new list on each iteration
var paper = new List<string>();
for (int i = 0; i < node.ChildNodes.Count; i++)
{
paper.Add(node.ChildNodes[i].InnerText);
}
papers.Add(paper);
}
return papers;
}
Also, using System.Linq extention methods, your code can be reduced to:
static List<List<string>> GetChildrenInnerTexts(XmlNodeList nodes)
{
return nodes.Cast<XmlNode>()
.Select(node => node.ChildNodes.Cast<XmlNode>()
.Select(child => child.InnerText)
.ToList())
.ToList();
}

The issue is with reference. You need to initialize 'paper' instead of clearing it.
Inside you first foreach loop, change
paper.Clear()
With
paper = new List<string>();
When you clear the object, you are keeping the reference to empty object for every index of papers

How do I store the initial state of a list of objects so that I can compare them to an updated list?

I have a list that is constantly being updated throughout my program. I would like to be able to compare the initial count and final count of my list after every update. The following is just a sample code (the original code is too lengthy) but it sufficiently captures the problem.
class Bot
{
public int ID { get; set; }
}
public class Program
{
public void Main()
{
List<Bot> InitialList = new List<Bot>();
List<Bot> FinalList = new List<Bot>();
for (int i = 0; i < 12345; i++)
{
Bot b = new Bot() {ID = i};
InitialList.Add(b);
}
FinalList = InitialList;
for (int i = 0; i < 12345; i++)
{
Bot b = new Bot() {ID = i};
FinalList.Add(b);
}
Console.Write($"Initial list has {InitialList.Count} bots");
Console.Write($"Final list has {FinalList.Count} bots");
}
}
Output:
Initial list has 24690 bots
Final list has 24690 bots
Expected for both lists to have 12345 bots.
What is correct way to copy the initial list so new set is not simply added to original?

To do what you seem to want to do, you want to copy the list rather than assign a new reference to the same list. So instead of
FinalList = InitialList;
Use
FinalList.AddRange(InitialList);
Basically what you had was two variables both referring to the same list. This way you have two different lists, one with the initial values and one with new values.
That said, you could also just store the count if that's all you want to do.
int initialCount = InitialList.Count;
FinalList = InitialList;
Although there's now no longer a reason to copy from one to the other if you already have the data you need.
I get the feeling you actually want to do more than what's stated in the question though, so the correct approach may change depending on what you actually want to do.

Unable to store values in a nested Dictionary

I am trying to store movie ratings by users in a Dictionary. The file from which the data is acquired is of the form
UserID | MovieID | Rating | Timestamp
They are tab separated values
//Take the first 100 lines from the file and store each line as a array element of text
string[] text = System.IO.File.ReadLines(#File path).Take(100).ToArray();
//extDic[username] - [moviename][rating] is the structure
Dictionary<string,Dictionary<string,double>> extDic=new Dictionary<string,Dictionary<string,double>>();
Dictionary<string, double> movie=new Dictionary<string,double>();
foreach(string s in text)
{
int rating;
string username=s.Split('\t')[0];
string moviename=s.Split('\t')[1];
Int32.TryParse(s.Split('\t')[2], out rating);
movie.Add(moviename,rating);
if (extDic.ContainsKey(username))
{
//Error line
extDic[username].Add(moviename, rating);
}
else
{
extDic.Add(username, movie);
}
movie.Clear();
}
I get the following error "An item with the same key has already been added" on the error line. I understand what the error is and have tried to solve it by checking with an if statement. However that doesn't solve it.
Also, I wonder if there is a significant of movie.clear()?

There must be duplicates of that user and movie.
To fix the error, you can use this for your "error line":
extDic[username][moviename] = rating;
Though there may be other problems afoot.

The problem might be caused by the fact that you are using the variable movie as a value for all the entries in the extDic dictionary. movie is nothing but a reference, so when you are doing a movie.Clear() you are clearing all the values from extDic.
You could entirely remove the variable movie and replace it with a fresh instance of new Dictionary<string, double>()
string[] text = System.IO.File.ReadLines(#File path).Take(100).ToArray();
//extDic[username] - [moviename][rating] is the structure
Dictionary<string,Dictionary<string,double>> extDic=new Dictionary<string,Dictionary<string,double>>();
foreach(string s in text)
{
int rating;
//split only once
string[] splitted = s.Split('\t');
//UPDATE: skip the current line if the structure is not ok
if(splitted.Length != 3){
continue;
}
string username=splitted[0];
string moviename=splitted[1];
Int32.TryParse(splitted[2], out rating);
//UPDATE: skip the current line if the user name or movie name is not valid
if(string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(moviename)){
continue;
}
if(!extDic.ContainsKey(username)){
//create a new Dictionary for every new user
extDic.Add(username, new Dictionary<string,double>());
}
//at this point we are sure to have all the keys set up
//let's assign the movie rating
extDic[username][moviename] = rating;
}

Your problem is that you are adding the same dictionary to all users so when two users have rated the same movie you will see this exception
int rating;
var result = from line in text
let tokens = s.Split('\t')
let username=tokens[0];
let moviename=tokens[1];
where Int32.TryParse(tokens[2], out rating);
group new {username, Rating=new{moviename,rating}} by username;
The above code will give you a structure that from a tree perspective is similar to your own. If you need the lookup capability you can simply call .ToDictionary
var extDic = result.ToDictionary(x=x.Key, x=>x.ToDictonary(y=>y.moviename,y=>y.rating))
The reason why I rewrote it in to LINQ is that it's a lot hard to make those kinds of mistakes using something that's side effect free like LINQ

Flat file normalization with a dynamic number of columns

I have a flat file with an unfortunately dynamic column structure. There is a value that is in a hierarchy of values, and each tier in the hierarchy gets its own column. For example, my flat file might resemble this:
StatisticID|FileId|Tier0ObjectId|Tier1ObjectId|Tier2ObjectId|Tier3ObjectId|Status
1234|7890|abcd|efgh|ijkl|mnop|Pending
...
The same feed the next day may resemble this:
StatisticID|FileId|Tier0ObjectId|Tier1ObjectId|Tier2ObjectId|Status
1234|7890|abcd|efgh|ijkl|Complete
...
The thing is, I don't care much about all the tiers; I only care about the id of the last (bottom) tier, and all the other row data that is not a part of the tier columns. I need normalize the feed to something resembling this to inject into a relational database:
StatisticID|FileId|ObjectId|Status
1234|7890|ijkl|Complete
...
What would be an efficient, easy-to-read mechanism for determining the last tier object id, and organizing the data as described? Every attempt I've made feels kludgy to me.
Some things I've done:
I have tried to examine the column names for regular expression patterns, identify the columns that are tiered, order them by name descending, and select the first record... but I lose the ordinal column number this way, so that didn't look good.
I have placed the columns I want into an IDictionary<string, int> object to reference, but again reliably collecting the ordinal of the dynamic columns is an issue, and it seems this would be rather non-performant.

I ran into a simular problem a few years ago. I used a Dictionary to map the columns, it was not pretty, but it worked.
First make a Dictionary:
private Dictionary<int, int> GetColumnDictionary(string headerLine)
{
Dictionary<int, int> columnDictionary = new Dictionary<int, int>();
List<string> columnNames = headerLine.Split('|').ToList();
string maxTierObjectColumnName = GetMaxTierObjectColumnName(columnNames);
for (int index = 0; index < columnNames.Count; index++)
{
if (columnNames[index] == "StatisticID")
{
columnDictionary.Add(0, index);
}
if (columnNames[index] == "FileId")
{
columnDictionary.Add(1, index);
}
if (columnNames[index] == maxTierObjectColumnName)
{
columnDictionary.Add(2, index);
}
if (columnNames[index] == "Status")
{
columnDictionary.Add(3, index);
}
}
return columnDictionary;
}
private string GetMaxTierObjectColumnName(List<string> columnNames)
{
// Edit this function if Tier ObjectId is greater then 9
var maxTierObjectColumnName = columnNames.Where(c => c.Contains("Tier") && c.Contains("Object")).OrderBy(c => c).Last();
return maxTierObjectColumnName;
}
And after that it's simply running thru the file:
private List<DataObject> ParseFile(string fileName)
{
StreamReader streamReader = new StreamReader(fileName);
string headerLine = streamReader.ReadLine();
Dictionary<int, int> columnDictionary = this.GetColumnDictionary(headerLine);
string line;
List<DataObject> dataObjects = new List<DataObject>();
while ((line = streamReader.ReadLine()) != null)
{
var lineValues = line.Split('|');
string statId = lineValues[columnDictionary[0]];
dataObjects.Add(
new DataObject()
{
StatisticId = lineValues[columnDictionary[0]],
FileId = lineValues[columnDictionary[1]],
ObjectId = lineValues[columnDictionary[2]],
Status = lineValues[columnDictionary[3]]
}
);
}
return dataObjects;
}
I hope this helps (even a little bit).

Personally I would not try to reformat your file. I think the easiest approach would be to parse each row from the front and the back. For example:
itemArray = getMyItems();
statisticId = itemArray[0];
fileId = itemArray[1];
//and so on for the rest of your pre-tier columns
//Then get the second to last column which will be the last tier
lastTierId = itemArray[itemArray.length -1];
Since you know the last tier will always be second from the end you can just start at the end and work your way forwards. This seems like it would be much easier than trying to reformat the datafile.
If you really want to create a new file, you could use this approach to get the data you want to write out.

I don't know C# syntax, but something along these lines:
split line in parts with | as separator
get parts [0], [1], [length - 2] and [length - 1]
pass the parts to the database handling code

how to dissect string values

How can I dissect or retrieve string values?
Here's the sample code that I'm working on now:
private void SplitStrings()
{
List<string> listvalues = new List<string>();
listvalues = (List<string>)Session["mylist"];
string[] strvalues = listvalues.ToArray();
for (int x = 0; x < strvalues.Length; x++)
{
}
}
Now that I'am able to retrieve list values in my session. How can I separately get the values of each list using foreach or for statement?
What I want to happen is to programmatically split the values of the strings depending on how many is in the list.

If you have a list of string values, you can do the following:
private void SplitStrings()
{
List<string> listValues = (List<string>) Session["mylist"];
// always check session values for null
if(listValues != null)
{
// go through each list item
foreach(string stringElement in listValues)
{
// do something with variable 'stringElement'
System.Console.WriteLine(stringElement);
}
}
}
Note that I test the result of casting the session and that I don't create a new list first-off, which is not necessary. Also note that I don't convert to an array, simply because looping a list is actually easier, or just as easy, as looping an array.
Note that you named your method SplitStrings, but we're not splitting anything. Did you mean to split something like "one;two;three;four" in a four-element list, based on the separator character?

I'm not sure what you're trying to obtain in this code, I don't know why you're converting your List to an Array.
You can loop through your listValues collection with a foreach block:
foreach(string value in listValues)
{
//do something with value, I.e.
Response.Write(value);
}

I don't know what's in the strings but you can start by simplifying. There is no point allocating a new List if you're going to overwrite it immediately.
private void SplitStrings()
{
List<string> list = (List<string>)Session["mylist"];
foreach(string value in list)
{
}
}

List listvalues = (List)Session["mylist"];
foreach (string s in listvalues)
{
//do what you want with s here
}