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Left join and count based on multiple values using linq c#

I have 2 lists. List A consists of this value,
status | level
-----------------
open | low
open | medium
open | high
closed | low
closed | medium
closed | high
List B consists of this value,
task | status | level
------------------------
A | open | low
B | open | medium
C | closed | high
D | closed | low
E | open | low
I want to do left join (all value inside list A must be in the new list), and count the number of tasks with related to status. I want the level value as well since it will be used later in my code. The expected output:
status | level | count
-------------------------
open | low | 2
open | medium | 1
open | high | 0
closed | low | 1
closed | medium | 0
closed | high | 1
I know there are many answers here which provides the ways to code, but I'm still stuck, because my code doesnt work, it seems like it does not do the group by method because when I count, the value shown is one for all status.
var joined3 = (from id1 in joined
join id2 in tr
on new { lev = id1.Key.ToString(), stat = id1.Value.ToString() } equals new { lev = id2.Level.ToString(), stat = id2.Status.ToString() } into grouped
from id2 in grouped.DefaultIfEmpty()
group id2 by new {level = id1.Key, status = id1.Value } into grouped
select new
{
level = grouped.Key.level,
status = grouped.Key.status,
count = grouped.Count()
}).ToList();

The problem is that because of the left-join semantics of DefaultIfEmpty(), you always have at least one row. So you need to add a predicate to the Count()
var joined3 = (
from id1 in joined
join id2 in tr
on new { lev = id1.Key, stat = id1.Value } equals new { lev = id2.Level, stat = id2.Status } into grouped
from id2 in grouped.DefaultIfEmpty()
group id2 by new {level = id1.Key, status = id1.Value } into grouped
select new
{
level = grouped.Key.level,
status = grouped.Key.status,
count = grouped.Count(id2 => id2.Key != null)
}).ToList();
Alternatively, a simpler method is: don't group, but instead use a correlated count of the other list
var joined3 = (
from id1 in joined
select new
{
level = id1.level,
status = id1.status,
count = tr.Count(id2 => id2.Key == id1.Key && id2.Value == id1.Value)
}).ToList();
I see no reason to use ToString here, and it is likely to impact performance. Key and Value should be the same type on each list/table respectively.

var list1 = new List<Type1>
{
new Type1() {Status = StatusEnum.Open, Level = LevelEnum.Low},
new Type1() {Status = StatusEnum.Open, Level = LevelEnum.Medium},
new Type1() {Status = StatusEnum.Open, Level = LevelEnum.High},
new Type1() {Status = StatusEnum.Closed, Level = LevelEnum.Low},
new Type1() {Status = StatusEnum.Closed, Level = LevelEnum.Medium},
new Type1() {Status = StatusEnum.Closed, Level = LevelEnum.High}
};
var list2 = new List<Type2>
{
new Type2() {TaskDescription = "A", Status = StatusEnum.Open, Level = LevelEnum.Low},
new Type2() {TaskDescription = "B", Status = StatusEnum.Open, Level = LevelEnum.Medium},
new Type2() {TaskDescription = "C", Status = StatusEnum.Closed, Level = LevelEnum.High},
new Type2() {TaskDescription = "D", Status = StatusEnum.Closed, Level = LevelEnum.Low},
new Type2() {TaskDescription = "E", Status = StatusEnum.Open, Level = LevelEnum.Low}
};
var list3 = new List<Type3>();
foreach (var t in list1)
{
list3.Add(new Type3()
{Level = t.Level, Status = t.Status, Count = list2.Count(x => x.Level == t.Level && x.Status == t.Status)});
}
foreach (var t in list3)
{
Console.WriteLine($"{t.Status}/{t.Level}/{t.Count}");
}
class Type1
{
public StatusEnum Status { get; set; }
public LevelEnum Level { get; set; }
}
class Type2 : Type1
{
public string TaskDescription { get; set; }
}
class Type3 : Type2
{
public int Count { get; set; }
}
public enum StatusEnum
{
Open,
Closed
}
public enum LevelEnum
{
Low,
Medium,
High
}

How to get average value using LEFT JOIN in LINQ and Lambda

I want to display each book average rating with its publisher using LINQ and Lambda.
Here's my book list
private List<Book> Books = new List<Book>(){
new Book {
Id: 1,
Name: Book A,
PublisherId: 1
}, new Book {
Id: 2,
Name: Book B,
PublisherId: 2
}, new Book {
Id: 3,
Name: Book C,
PublisherId: 1
}
};
First, i Join Book list with Publisher list using this query
var bookPublisher = Books.SelectMany( book => Publishers.Where(publisher => book.PublisherId == publisher.Id),
(book, publisher) => new { book, publisher });
Then, i try to use left join with BookTransaction list to get detail rating for each book. Here's my BookTransaction list.
private List<Book_Transaction> BookTransactions = new List<Book_Transaction>() {
new Book_Transaction {
Id = 1,
BookId = 1,
CustomerId = 1,
RatingStar = 4.5
}, new Book_Transaction {
Id = 2,
BookId = 2,
CustomerId = 1,
RatingStar = 4
}, new Book_Transaction {
Id = 3,
BookId = 1,
CustomerId = 2,
RatingStar = 5
},new Book_Transaction {
Id = 4,
BookId = 2,
CustomerId = 2,
RatingStar = 3.5
},new Book_Transaction {
Id = 5,
BookId = 1,
CustomerId = 3,
RatingStar = 4
}};
and here's my query
var bookPublisherRating = bookPublisher.SelectMany(bp => BookTransactions.Where(bt => bp.book.Id == bt.BookId).DefaultIfEmpty(),
(bp, bt) => new { BookPublish = bp, BookRating = bt.RatingStar });
in that query, i got the error saying that "'Object reference not set to an instance of an object.' bt was null."
I tried using different approach, but the result it just the same error.
var bookPublisherRating = bookPublisher.GroupJoin(BookTransactions,
bp => bp.book.Id,
bt => bt.BookId,
(bp, bt) => new { BookPublish = bp, BookTrans = bt })
.SelectMany(temp => temp.BookTrans.DefaultIfEmpty(),
(temp, y) => new { BookPublish = temp.BookPublish, bookRating = y.RatingStar });
Can someone tell me where i was wrong? When i deleted the DefaultIfEmpty function, it can display the data but only where both list have the bookId value included, like this
| BookName | PublisherName | Rating |
| Book A | Publisher A | 4.5 |
| Book A | Publisher A | 5 |
| Book A | Publisher A | 4 |
| Book B | Publisher B | 4 |
| Book B | Publisher B | 3.5 |
I expect the result of the query just like this
| BookName | PublisherName | Rating |
| Book A | Publisher A | 4.5 |
| Book B | Publisher B | 3.75 |
| Book C | Publisher A | 0 |

Linq has an Average Method. You can call it on a collection of numeric values, or for a collection of objects you can pass it the property name to average. You can also call GroupBy to create key<->collection pairs.
So you can group your data by the BookId and find the average rating.
Assuming the following
public class Book_Transaction
{
public int Id { get; set; }
public int BookId { get; set; }
public int CustomerId { get; set; }
public double RatingStar { get; set; }
}
var bookTransactions = new List<Book_Transaction>() {
new Book_Transaction {
Id = 1,
BookId = 1,
CustomerId = 1,
RatingStar = 4.5
}, new Book_Transaction {
Id = 2,
BookId = 2,
CustomerId = 1,
RatingStar = 4
}, new Book_Transaction {
Id = 3,
BookId = 1,
CustomerId = 2,
RatingStar = 5
},new Book_Transaction {
Id = 4,
BookId = 2,
CustomerId = 2,
RatingStar = 3.5
},new Book_Transaction {
Id = 5,
BookId = 1,
CustomerId = 3,
RatingStar = 4
}};
Then
bookTransactions.GroupBy(
bt => bt.BookId,
(bookId, collection) => new {
BookId = bookId,
AverageRating = collection.Average(x => x.RatingStar)
}).ToList()
Gives the following output in the C# interactive console:
List<<>f__AnonymousType0#5<int, double>>(2) {
{ BookId = 1, AverageRating = 4.5 },
{ BookId = 2, AverageRating = 3.75 }
}

Take and Group By in EntityFramework [duplicate]

This question already has an answer here:
Take(limit) list inside Groupby in Entity Framework
(1 answer)
Closed 5 years ago.
I need to take (for example, 2), 2 messages from a conversation
example:
id = idConversation
Id | messageId | Message
---|-----------|--------
1 | 1 | "asd"
1 | 2 | "asd2"
1 | 3 | "asd3"
1 | 4 | "asd4"
2 | 5 | "asd5"
3 | 6 | "asd6"
3 | 7 | "asd7"
3 | 8 | "asd8"
3 | 9 | "asd9"
3 | 10 | "asd10"
4 | 11 | "asd11"
4 | 12 | "asd12"
4 | 13 | "asd13"
and i want that
Id messageId Message
---|-----------|--------
1 | 1 | "asd"
1 | 2 | "asd2"
2 | 5 | "asd5"
3 | 6 | "asd6"
3 | 7 | "asd7"
4 | 11 | "asd11"
4 | 12 | "asd12"
i can grouby idConversation, but i cant limit quantity using grouby in a conversation.
var test = unitOfWork.ChatMensagemRepository.GetAll()
.Where(x => x.PessoaCodigoPessoa == codigoRemetente)
.GroupBy(x => x.ChatConversaCodigoChatConversa)
.Select(group => new
{
codigoChat = group.Key,
list = group.Select(mensagem => new
{
// do stuff
})
}).ToList();
this is ok... but dont limit my list, when i do group.take(2).Select.....
give me "Subquery returns more than 1 row"
var test = unitOfWork.ChatMensagemRepository.GetAll()
.Where(x => x.PessoaCodigoPessoa == codigoRemetente)
.GroupBy(x => x.ChatConversaCodigoChatConversa)
.Select(group => new
{
codigoChat = group.Key,
list = group.Take(2).Select(mensagem => new
{
// do stuff
})
}).ToList();
error : Subquery returns more than 1 row
var test = unitOfWork.ChatMensagemRepository.GetAll()
.Where(x => x.PessoaCodigoPessoa == codigoRemetente)
.GroupBy(x => x.ChatConversaCodigoChatConversa)
.Select(group => new
{
codigoChat = group.Key,
list = group.Select(mensagem => new
{
// do stuff
}).take(2)
}).ToList();
error : Subquery returns more than 1 row

Here's an example of what I think you're after. This query will return the top 3 sudtents by GPA in each class:
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Ef6Test
{
class Student
{
public int Id { get; set; }
public string Name { get; set; }
public string Class{ get; set; }
public decimal GPA { get; set; }
}
class Db : DbContext
{
public DbSet<Student> Students { get; set; }
}
class Program
{
static void Main(string[] args)
{
using (var db = new Db())
{
var q = db.Students
.GroupBy(s => s.Class)
.SelectMany(g => g.OrderByDescending(s => s.GPA).Take(3));
Console.WriteLine(q.ToString());
Console.ReadKey();
}
}
}
}

I tried this code and is working fine:
class Conversation
{
public int Id;
public string Message;
public int MessageId;
}
class Program
{
static void Main(string[] args)
{
var inputList = new List<Conversation>
{
new Conversation() {Id = 1, Message = "asd0", MessageId = 1},
new Conversation() {Id = 1, Message = "asd1", MessageId = 2},
new Conversation() {Id = 1, Message = "asd2", MessageId = 3},
new Conversation() {Id = 2, Message = "asd3", MessageId = 4},
new Conversation() {Id = 2, Message = "asd4", MessageId = 5},
new Conversation() {Id = 2, Message = "asd5", MessageId = 6},
new Conversation() {Id = 3, Message = "asd6", MessageId = 7}
};
var outputList = inputList.GroupBy(x => x.Id)
.SelectMany(x => x.OrderBy(y => y.MessageId).Take(2).ToList())
.ToList();
Console.ReadKey();
}
}

Dynamically Pivot in LINQ: Pivoted Columns Determined at Runtime

Let's say I have three tables. Basically, one table of things, one table describing the possible attributes of the things, and a bridge table providing the values for those attributes for a particular thing. This lets you do dynamic metadata.
Users can add metadata properties at any time, and then they can provide values for those properties for any thing in the "things" table.
So like this:
Table: Persons
PersonID | FirstName | LastName
1 | Bob | Jones
2 | Fred | Smith
3 | Sally | Doe
Table: Properties
PropertyID | Name
1 | SupervisorName
2 | Age
3 | Birthday
4 | EmployeeNumber
5 | Hometown
Table: PropertyValues
PersonID | PropertyID | PropertyValue
1 | 1 | Frank Grimes
1 | 2 | 47
2 | 2 | 35
2 | 4 | 1983738
2 | 3 | 5/5/1978
3 | 3 | 4/4/1937
3 | 5 | Chicago, IL
So, users want to be able to view a report of these properties. Maybe I want to see a table containing the age and birthday of all employees. There would be blanks in the table if those values aren't populated for those users. Then maybe I want to see a report that includes supervisor, age and birthday--I should be able to generate that table on the fly as well.
Now, in order to do this with SQL, I would dynamically construct a query and add a join to that query for each property that I want to pivot up to the top. That's how it works now.
If I wanted to do this in LINQ, and I knew which properties to pivot while writing the code, I could do that too--I'd just use GroupJoin().
What I don't know is how to dynamically construct a LINQ query that would allow me to pivot any number of properties at runtime, without knowing what they are ahead of time.
Any ideas?
(Before you knee-jerk mark this as a duplicate, know that I did a fair amount of StackOverflow research before posting this question, and if this exact question has been asked before, I couldn't find it.)

You can build linq expression trees dynamically. This topic is covered (including example) in the following MSDN article: http://msdn.microsoft.com/en-us/library/bb882637.aspx
My suggestion would be to write an example Linq query for your task and rebuild it programmatically with expression trees. Once it works you adapt it and inject your dynamic parts.

My thought is you could join with a where condition as follows:
Person Class
public class Person
{
public int Id {get; set;}
public string FirstName {get; set;}
public string LastName {get; set;}
}
Property Class
public class Property
{
public int Id {get; set;}
public string Name {get; set;}
}
Value Class
public class Value
{
public int PersonId {get; set;}
public int PropertyId {get; set;}
public string Val {get; set;}
}
Code
void Main()
{
var selectBy = "Birthday";
var persons = new List<Person>() { new Person {Id = 1, FirstName = "Bob", LastName = "Jones"}, new Person {Id = 2, FirstName = "Fred", LastName = "Smith"}, new Person {Id = 3,FirstName = "Sally", LastName = "Doe"}};
var properties = new List<Property>() { new Property {Id = 1, Name = "SupervisorName"}, new Property {Id = 2, Name = "Age"}, new Property {Id = 3, Name = "Birthday"}, new Property {Id = 4, Name = "EmployeeNumber"}, new Property {Id = 5, Name = "Hometown"}};
var values = new List<Value>() { new Value {PersonId = 1, PropertyId = 1, Val="Frank Grimes"}, new Value {PersonId = 1, PropertyId = 2, Val="47"}, new Value {PersonId = 2, PropertyId = 2, Val="35"}, new Value {PersonId = 2, PropertyId = 4, Val="1983738"}, new Value {PersonId = 2, PropertyId = 3, Val="5/5/1978"}, new Value {PersonId = 3, PropertyId = 3, Val="4/4/1937"}, new Value {PersonId = 3, PropertyId = 5, Val="Chicago, IL"}};
var result = from v in values
join p in persons on v.PersonId equals p.Id
join p2 in properties on v.PropertyId equals p2.Id
where p2.Name.Equals(selectBy)
select new { Name = p.FirstName + " " + p.LastName,
Value = v.Val
};
result.Dump();
}
Results
Name, Value
Fred Smith 5/5/1978
Sally Doe 4/4/1937
Revised Answer
void Main()
{
var selectBy = "Birthday";
var persons = new List<Person>() { new Person {Id = 1, FirstName = "Bob", LastName = "Jones"}, new Person {Id = 2, FirstName = "Fred", LastName = "Smith"}, new Person {Id = 3,FirstName = "Sally", LastName = "Doe"}};
var properties = new List<Property>() { new Property {Id = 1, Name = "SupervisorName"}, new Property {Id = 2, Name = "Age"}, new Property {Id = 3, Name = "Birthday"}, new Property {Id = 4, Name = "EmployeeNumber"}, new Property {Id = 5, Name = "Hometown"}};
var values = new List<Value>() { new Value {PersonId = 1, PropertyId = 1, Val="Frank Grimes"}, new Value {PersonId = 1, PropertyId = 2, Val="47"}, new Value {PersonId = 2, PropertyId = 2, Val="35"}, new Value {PersonId = 2, PropertyId = 4, Val="1983738"}, new Value {PersonId = 2, PropertyId = 3, Val="5/5/1978"}, new Value {PersonId = 3, PropertyId = 3, Val="4/4/1937"}, new Value {PersonId = 3, PropertyId = 5, Val="Chicago, IL"}};
// Default Values for the Cartesian Product
var defaultValues = new string[]{"","","","",""};
// propertyKeys are used to filter values generated for pivot table
var propertyKeys = new List<Property> { new Property{Id=1}, new Property{Id=2}, new Property{Id=3}};
// Generate default values for every person and each property
var cartesianProduct = from ppl in persons
from prop in properties
join pk in propertyKeys on prop.Id equals pk.Id
select new {PersonId = ppl.Id, PropertyId = prop.Id, Val = defaultValues[prop.Id-1]};
// Create Pivot Values based on selected PropertyIds
var newValues = from cp in cartesianProduct
join v in values on new {cp.PersonId, cp.PropertyId} equals new { v.PersonId, v.PropertyId } into gj
from x in gj.DefaultIfEmpty()
select new {
PersonId = (x == null ? cp.PersonId : x.PersonId),
PropertyId = (x == null ? cp.PropertyId: x.PropertyId),
Val = ( x == null ? cp.Val : x.Val )
};
foreach( var y in newValues )
{
var aPerson = persons.Where( r=> r.Id == y.PersonId ).First().FirstName;
var aProperty = properties.Where( r=> r.Id == y.PropertyId ).First().Name;
Console.WriteLine(string.Format("{0:12} {1:12} {2:12}", aPerson, aProperty, y.Val));
}
}
Results:
Bob | SupervisorName | Frank Grimes
Bob | Age | 47
Bob | Birthday |
Fred | SupervisorName |
Fred | Age | 35
Fred | Birthday | 5/5/1978
Sally | SupervisorName |
Sally | Age |
Sally | Birthday | 4/4/1937

Get child record using Linq

This is my first time to hear about LINQ and I have no idea about it. Please be gentle on me.
I have this set of data.
+---------+--------+---------------+
| RadioID | NodeID | SourceRadioID |
+---------+--------+---------------+
| R0 | 1 | |
| R1 | 1 | |
| R2 | 1 | |
| R3 | 1 | |
| R4 | 1 | |
| R5 | 2 | |
| R6 | 2 | |
| R7 | 2 | R0 |
| R8 | 2 | |
| R9 | 2 | |
| R10 | 11 | |
| R11 | 11 | R9 |
| R12 | 11 | |
| R13 | 11 | |
+---------+--------+---------------+
What I need to do is to write a method that returns a list of NodeID. example,
List<int> dependentNode = GetChildNode(1); // int ParentNode
My expected results are NodeIDs: 2 and 11.
NodeID = 2 is included because there is a RadioID = R7 that is connected to RadioID = R0 which belongs to NodeID = 1.
NodeID = 11 is also included because RadioID = R11 is connected to Radio = R9 which belongs to NodeID = 2 (which is also connected to NodeID = 1).
I lookup this article but I always get StackOverFlowException
Rendering a hierarchy using LINQ
Here's the full code:
public class RadioEntity
{
public string RadioID { get; set; }
public int NodeID { get; set; }
public string SourceRadioID { get; set; }
}
public class SampleDemo
{
public void SampleMethod()
{
Func<int, int,List<int>> GetChildNode = null;
GetChildNode = (x, y) =>
{
return (from _x in GetRadio()
where (GetRadio().Where(i => i.NodeID == x).Select(i => i.RadioID)).Contains(_x.RadioID)
from _y in new[] { _x.NodeID }.Union(GetChildNode(_x.NodeID, y + 1))
select _y).ToList<int>();
};
var _res = GetChildNode(1, 0);
}
public List<RadioEntity> GetRadio()
{
List<RadioEntity> _returnVal = new List<RadioEntity>();
_returnVal.Add(new RadioEntity() { RadioID = "R0", NodeID = 1, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R1", NodeID = 1, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R2", NodeID = 1, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R3", NodeID = 1, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R4", NodeID = 1, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R5", NodeID = 2, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R6", NodeID = 2, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R7", NodeID = 2, SourceRadioID = "R0" });
_returnVal.Add(new RadioEntity() { RadioID = "R8", NodeID = 2, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R9", NodeID = 2, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R10", NodeID = 11, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R11", NodeID = 11, SourceRadioID = "R9" });
_returnVal.Add(new RadioEntity() { RadioID = "R12", NodeID = 11, SourceRadioID = "" });
_returnVal.Add(new RadioEntity() { RadioID = "R13", NodeID = 11, SourceRadioID = "" });
return _returnVal;
}
}
You can suggest if there is much better way to do it. Sorry Newbie here.

If you are newbie dont be too clever with recursion and lambdas.
public List<int> GetChildren(int id)
{
var nodes = GetRadio();
var parent = nodes.Single(n => n.NodeID == id);
var children = nodes.Where(n => n.SourceRadioID == parent.RadioID).Select(n => n.NodeID);
return children.Union(children.SelectMany(GetChildren)).ToList();
}
UPDATE 1
public List<int> GetChildren(int id)
{
IEnumerable<RadioEntity> parent = GetRadio().Where(x => x.NodeID == id);
IEnumerable<int> children = (
from r in GetRadio()
where parent.Select(x=>x.RadioID)
.Contains(r.SourceRadioID)
select r
).Select(n => n.NodeID);
return children.Union(children.SelectMany(GetChildren)).ToList();
}