We Keep Coding

How to pass Dictionary TKey and TValue to a method one by one in C#

I have a Dictionary in code as:
SqlCommand query = con.CreateCommand();
query.CommandText = #"select pid, p_title from sub_aminer_paper where pid IN (/*a long list of Pid's*/)";
SqlDataReader reader = query.ExecuteReader();
Dictionary<int, string> paper_title = new Dictionary<int, string>();
paper_title.Add(Convert.ToInt32(reader["pid"]), reader["p_title"].ToString() );
And string lines reading a text file as:
var lines = System.IO.File.ReadLines(#"D:\~\research_fields.txt");
I want to pass Dictionary TKey and TValue to a method to be called in a HashSet as:
var similarity = new HashSet<Tuple<string, double, int>>();
similarity.Add(lines.Select(line => Tuple.Create(line, p.calculate_CS(line, paper_title.Select(item => item.Value).ToString()), paper_title.Select(item => item.Key))));
But this line of code giving error of some invalid arguments.
The method p.calculate_CS(string, string) takes two arguments of type string. I have to take one string from lines and one string from Dictionary i.e. paper_title. The third argument for Tuple is of type int that will be the Key from Dictionary.
Please help in this regard. Thanks!

From the discussion in comments, I think your code should look something like
var similarity = new HashSet<Tuple<string, double, int>>();
foreach(var key in paper_title.Keys){
similarity.Add(lines.Select(line => Tuple.Create(line,
p.calculate_CS(line, paper_title[key]), key)));
}
This code will iterate through each key in your dictionary and will call calculate_CS method with appropriate attributes.

The TKey and TValue can be passed one by one to method using following:
Dictionary<int, string> paper_title = new Dictionary<int, string>();
paper_title.Add(Convert.ToInt32(reader["pid"]), reader["p_title"].ToString() );
var similarity = new HashSet<Tuple<string, double, int>>();
foreach(KeyValuePair<int, string> item in paper_title)
{
similarity.UnionWith(lines.Select(line => Tuple.Create(line, p.calculate_CS(line, item.Value), item.Key)));
}

Convert dictionary with List to IEnumerable

I have a dictionary:
Dictionary<String, List<Foo>> test = new Dictionary<String, List<Foo>>();
I then populate this dictionary hence why I need the list so I can call Add(). My problem is the function needs to return:
Dictionary<String, IEnumerable<Foo>>
Is there any easy way to do this without doing the obvious and looping through my original dictionary and doing it manually?

return dictionary.ToDictionary(x => x.Key,x => x.Value.AsEnumerable())

It's more efficient and easier to use the List<Foo> to add things but add it to a Dictionary<String, IEnumerable<Foo>>. That's no problem since List<Foo> implements IEnumerable<Foo>, it's not even necessary to cast.
So something like this(pseudo code):
var test = new Dictionary<String, IEnumerable<Foo>>();
foreach(var x in something)
{
var list = new List<Foo>();
foreach(var y in x.SomeCollection)
list.Add(y.SomeProperty);
test.Add(x.KeyProperty, list); // works since List<T> is also an IEnumerable<T>
}

I tried this route as well, converting Dictionary<string, List<Foo>> to a ReadOnlyDictionary<string, IEnumerable<Foo>>. While I was trying to convert to a read-only dictionary, the whole purpose of converting a List to IEnumerable is to make a read only collection. The problem with the OP's approach is:
Dictionary<string, List<string>> errors = new Dictionary<string, List<string>>();
errors["foo"] = new List<string>() { "You can't do this" };
Dictionary<string, IEnumerable<string>> readOnlyErrors = // convert errors...
readOnlyErrors["foo"] = new List<string>() { "I'm not actually read-only!" };
The appearance of IEnumerable<Foo> makes you think this is read only and safe, when in fact it is not. After reading the question LINQ Convert Dictionary to Lookup a Lookup object is more appropriate, because it allows you to:
Associate one key with multiple values
You cannot overwrite a key with a new value
// This results in a compiler error
lookUp["foo"] = new List<Foo>() { ... };
The "multiple values" are already defined as IEnumerable<T>
You can still use the same outer and inner loop algorithm to extract individual values:
ILookup<string, string> lookup = // Convert to lookup
foreach (IGrouping<string, string> grouping in lookup)
{
Console.WriteLine(grouping.Key + ":");
foreach (string item in grouping)
{
Console.WriteLine(" item: " + item);
}
}
Convert Dictionary<string, List<Foo>> to ILookup<string, Foo>
It's a quick two-liner:
Dictionary<string, List<Foo>> foos = // Create and populate 'foos'
ILookup<string, Foo> lookup = foos.SelectMany(item => item.Value, Tuple.Create)
.ToLookup(p => p.Item1.Key, p => p.Item2);
Now you can use the same two-step loop as you would have with a Dictionary<string, IEnumerable<Foo>>:
foreach (IGrouping<string, Foo> grouping in lookup)
{
string key = grouping.Key;
foreach (Foo foo in grouping)
{
// Do stuff with key and foo
}
}
Source: LINQ Convert Dictionary to Lookup
Converting to another Dictionary with an IEnumerable value is like trying to stuff a square peg into a round hole. The more appropriate, and safe way (from an object-oriented standpoint) is to convert your read/write Dictionary to a Lookup. This gives you the true intended safety of an object that is read-only (except for the Foo items, which might not be immutable).
I would go so far as to say that most times when a ReadOnlyDictionary is used, you could use ILookup and get the same functionality.

define a List like List<int,string>?

I need a two column list like:
List<int,string> mylist= new List<int,string>();
it says
using the generic type System.collection.generic.List<T> requires 1 type arguments.

Depending on your needs, you have a few options here.
If you don't need to do key/value lookups and want to stick with a List<>, you can make use of Tuple<int, string>:
List<Tuple<int, string>> mylist = new List<Tuple<int, string>>();
// add an item
mylist.Add(new Tuple<int, string>(someInt, someString));
If you do want key/value lookups, you could move towards a Dictionary<int, string>:
Dictionary<int, string> mydict = new Dictionary<int, string>();
// add an item
mydict.Add(someInt, someString);

You could use an immutable struct
public struct Data
{
public Data(int intValue, string strValue)
{
IntegerData = intValue;
StringData = strValue;
}
public int IntegerData { get; private set; }
public string StringData { get; private set; }
}
var list = new List<Data>();
Or a KeyValuePair<int, string>
using Data = System.Collections.Generic.KeyValuePair<int, string>
...
var list = new List<Data>();
list.Add(new Data(12345, "56789"));

With the new ValueTuple from C# 7 (VS 2017 and above), there is a new solution:
List<(int,string)> mylist= new List<(int,string)>();
Which creates a list of ValueTuple type. If you're targeting .NET Framework 4.7+ or .NET/.NET Core, it's native, otherwise you have to get the ValueTuple package from nuget.
It's a struct opposing to Tuple, which is a class. It also has the advantage over the Tuple class that you could create a named tuple, like this:
var mylist = new List<(int myInt, string myString)>();
That way you can access like mylist[0].myInt and mylist[0].myString

Since your example uses a generic List, I assume you don't need an index or unique constraint on your data. A List may contain duplicate values. If you want to insure a unique key, consider using a Dictionary<TKey, TValue>().
var list = new List<Tuple<int,string>>();
list.Add(Tuple.Create(1, "Andy"));
list.Add(Tuple.Create(1, "John"));
list.Add(Tuple.Create(3, "Sally"));
foreach (var item in list)
{
Console.WriteLine(item.Item1.ToString());
Console.WriteLine(item.Item2);
}

Use C# Dictionary datastructure it good for you...
Dictionary<string, int> dict = new Dictionary<string, int>();
dict.Add("one", 1);
dict.Add("two", 2);
You can retrieve data from Ditionary in a simple way..
foreach (KeyValuePair<string, int> pair in dict)
{
MessageBox.Show(pair.Key.ToString ()+ " - " + pair.Value.ToString () );
}
For more example using C# Dictionary... C# Dictionary
Navi.

Not sure about your specific scenario, but you have three options:
1.) use Dictionary<..,..>
2.) create a wrapper class around your values and then you can use List
3.) use Tuple

List<Tuple<string, DateTime, string>> mylist = new List<Tuple<string, DateTime,string>>();
mylist.Add(new Tuple<string, DateTime, string>(Datei_Info.Dateiname, Datei_Info.Datum, Datei_Info.Größe));
for (int i = 0; i < mylist.Count; i++)
{
Console.WriteLine(mylist[i]);
}

For that, you could use a Dictionary where the int is the key.
new Dictionary<int, string>();
If you really want to use a list, it could be a List<Tuple<int,string>>() but, Tuple class is readonly, so you have to recreate the instance to modifie it.

Acquiring all values of nested dictionaries that contain the same key using Linq

I'm still trying to get a handle on LINQ, and while I do have a bit of an understanding for the simpler functions, stacking these eludes me to a certain extent, I'm hoping someone can lend me a hand.
I currently have a dictionary that is effectively:
Dictionary<Type, Dictionary<int, EntityComponent>> ComponentSystems
I'm trying to write a method that will return all instances of EntityComponent that have a given key, that is, if the parent dictionary contains two nested dictionaries and each of them have an entry with '1' as the key, the method will return the values that match said key as an IEnumerable<EntityComponent>
I've muched around with SelectMany and all the various other LINQ commands but I'm still struggling to figure it out.
As another example just to be clear, lets say I have the following setup:
Dictionary<object, Dictionary<int, string>> test =
new Dictionary<object, Dictionary<int, string>>();
Dictionary<int, string> test1 = new Dictionary<int, string>();
test1[1] = "test1-1";
test1[2] = "test1-2";
test[0] = test1;
Dictionary<int, string> test2 = new Dictionary<int, string>();
test2[1] = "test2-1";
test2[2] = "test2-2";
test[1] = test2;
Given that the key I'm looking for is '1', I would need to produce a linq statement that would return both "test1-1" and "test2-1".

int key = 1;
var query = test.Values // select inner dictionaries
.Where(d => d.ContainsKey(key)) // which contain your key
.Select(d => d[key]); // and return value by key
Returns:
"test1-1"
"test2-1"

Finding already existing value in Key Value pair

I am storing a string and int value in Key value pair.
var list = new List<KeyValuePair<string, int>>();
While adding i need to check if string(Key) already exists in list, if exists i need to add it to Value instead of adding new key.
How to check and add?

Instead of List you can use Dictionary and check if it contains key then add the new value to the existing key
int newValue = 10;
Dictionary<string, int> dictionary = new Dictionary<string, int>();
if (dictionary.ContainsKey("key"))
dictionary["key"] = dictionary["key"] + newValue;

use dictonary. Dictionary in C# and I suggest you to read this post Dictonary in .net
Dictionary<string, int> dictionary =
new Dictionary<string, int>();
dictionary.Add("cat", 2);
dictionary.Add("dog", 1);
dictionary.Add("llama", 0);
dictionary.Add("iguana", -1);
to check. use ContainsKey ContainsKey
if (dictionary.ContainsKey("key"))
    dictionary["key"] = dictionary["key"] + yourValue;

If you need use the list,you must foreach the list,and look for the keys.
Simplely,you can use hashtable.

For anyone who has to use a List (which was the case for me, since it does things Dictionary doesn't), you can just use a lambda expression to see if the List contains the Key:
list.Any(l => l.Key == checkForKey);

Your needs exactly describe the design of Dictionarys?
Dictionary<string, string> openWith =
new Dictionary<string, string>();
// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";

For sure, dictionary is preferable in your case. You can not modify the Value of KeyValue<string,int> class as it is Immutable.
But even if you still want to use List<KeyValuePair<string, int>>();. You can use IEqualityComparer<KeyValuePair<string, int>>. Code will be like.
public class KeyComparer : IEqualityComparer<KeyValuePair<string, int>>
{
public bool Equals(KeyValuePair<string, int> x, KeyValuePair<string, int> y)
{
return x.Key.Equals(y.Key);
}
public int GetHashCode(KeyValuePair<string, int> obj)
{
return obj.Key.GetHashCode();
}
}
And use it in Contains like
var list = new List<KeyValuePair<string, int>>();
string checkKey = "my string";
if (list.Contains(new KeyValuePair<string, int>(checkKey, int.MinValue), new KeyComparer()))
{
KeyValuePair<string, int> item = list.Find((lItem) => lItem.Key.Equals(checkKey));
list.Remove(item);
list.Add(new KeyValuePair<string, int>("checkKey", int.MinValue));// add new value
}
which does not sounds good way.
hope this info helps..