In this article, you will learn what is Group by query in LINQ in c#
In this post, How to use group by query in LINQ c#. The GroupBy operator returns a group of elements from the given collection based on some key value. Each group is represented by IGrouping<TKey, TElement> object.
Example:-
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace usingcsharp
{
class Program
{
static void Main(string[] args)
{
StudentClass sc = new StudentClass();
sc.QueryHighScores(2, 80);
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
public class StudentClass
{
protected enum GradeLevel { FirstYear = 2, SecondYear, ThirdYear, FourthYear };
protected class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int ID { get; set; }
public GradeLevel Year;
public List<int> ExamScores;
}
protected static List<Student> students = new List<Student>
{
new Student {FirstName = "Ram", LastName = "Kumar", ID = 1,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 90, 81, 81, 80}},
new Student {FirstName = "Amara", LastName = "Mishra", ID = 2,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 100, 87, 91, 93}},
new Student {FirstName = "Amartya", LastName = "Tiwari", ID = 3,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 94, 50, 80, 89}},
new Student {FirstName = "Ambaka", LastName = "Chaurasiya", ID = 4,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 98, 89, 86, 82}},
new Student {FirstName = "Alankrti", LastName = "Yadav", ID = 5,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 30, 71, 91, 71}},
new Student {FirstName = "Amaranayagan", LastName = "Gupta", ID = 6,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 92, 90, 86, 78}},
new Student {FirstName = "Amratav", LastName = "Prasad", ID = 7,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 88, 94, 65, 91}},
new Student {FirstName = "Arbhata", LastName = "Macho", ID = 8,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 75, 84, 20, 39}},
new Student {FirstName = "Arghya", LastName = "Thakur", ID = 9,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 97, 92, 80, 60}},
new Student {FirstName = "Apurva", LastName = "Verma", ID = 10,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 68, 80, 88, 92}},
new Student {FirstName = "Arib", LastName = "kumar", ID = 11,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 55, 92, 93, 90}},
new Student {FirstName = "Arjuna", LastName = "Singh", ID = 12,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 90, 10, 90, 40}}
};
}
}
}
protected static int GetPercentile(Student s)
{
double avg = s.ExamScores.Average();
return avg > 0 ? (int)avg / 10 : 0;
}
public void QueryHighScores(int exam, int score)
{
var highScores = from student in students
where student.ExamScores[exam] > score
select new { Name = student.FirstName, Score = student.ExamScores[exam] };
foreach (var item in highScores)
{
Console.WriteLine(string.Format("{0,-15}{1}", item.Name, item.Score));
}
}public void GroupBySubstring()
{
Console.WriteLine("\r\nGroup by something other than a property of the object:");
var queryFirstLetters =
from student in students
group student by student.LastName[0];
foreach (var studentGroup in queryFirstLetters)
{
Console.WriteLine(string.Format("Key: {0}"), studentGroup.Key);
// Nested foreach is required to access group items.
foreach (var student in studentGroup)
{
Console.WriteLine(string.Format("\t{0}, {1}"), student.LastName, student.FirstName);
}
}
} public void GroupBySingleProperty()
{
Console.WriteLine("Group by a single property in an object:");
// Variable queryLastNames is an IEnumerable<IGrouping<string,
// DataClass.Student>>.
var queryLastNames =
from student in students
group student by student.LastName into newGroup
orderby newGroup.Key
select newGroup;
foreach (var nameGroup in queryLastNames)
{
Console.WriteLine(string.Format("Key: {0}"), nameGroup.Key);
foreach (var student in nameGroup)
{
Console.WriteLine(string.Format("\t{0}, {1}"), student.LastName, student.FirstName);
}
}
}public void GroupByRange()
{
Console.WriteLine("\r\nGroup by numeric range and project into a new anonymous type:");
var queryNumericRange =
from student in students
let percentile = GetPercentile(student)
group new { student.FirstName, student.LastName } by percentile into percentGroup
orderby percentGroup.Key
select percentGroup;
// Nested foreach required to iterate over groups and group items.
foreach (var studentGroup in queryNumericRange)
{
Console.WriteLine(string.Format("Key: {0 * 10}"), studentGroup.Key);
foreach (var item in studentGroup)
{
Console.WriteLine(string.Format("\t{0}, {1}"), item.LastName, item.FirstName);
}
}
}public void GroupByBoolean()
{
Console.WriteLine("\r\nGroup by a Boolean into two groups with string keys");
Console.WriteLine("\"True\" and \"False\" and project into a new anonymous type:");
var queryGroupByAverages = from student in students
group new { student.FirstName, student.LastName }
by student.ExamScores.Average() > 75 into studentGroup
select studentGroup;
foreach (var studentGroup in queryGroupByAverages)
{
Console.WriteLine(string.Format("Key: {0}"), studentGroup.Key);
foreach (var student in studentGroup)
Console.WriteLine(string.Format("\t{0} {1}"), student.FirstName, student.LastName);
}
} public void GroupByCompositeKey()
{
var queryHighScoreGroups =
from student in students
group student by new
{
FirstLetter = student.LastName[0],
Score = student.ExamScores[0] > 85
} into studentGroup
orderby studentGroup.Key.FirstLetter
select studentGroup;
Console.WriteLine("\r\nGroup and order by a compound key:");
foreach (var scoreGroup in queryHighScoreGroups)
{
string s = scoreGroup.Key.Score == true ? "more than" : "less than";
Console.WriteLine(string.Format("Name starts with {0} who scored {s} 85"), scoreGroup.Key.FirstLetter);
foreach (var item in scoreGroup)
{
Console.WriteLine(string.Format("\t{0} {1}", item.FirstName, item.LastName));
}
}
}OR
You can paste the following code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace usingcsharp
{
class Program
{
static void Main(string[] args)
{
StudentClass sc = new StudentClass();
sc.QueryHighScores(2, 80);
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
public class StudentClass
{
protected enum GradeLevel { FirstYear = 2, SecondYear, ThirdYear, FourthYear };
protected class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int ID { get; set; }
public GradeLevel Year;
public List<int> ExamScores;
}
protected static List<Student> students = new List<Student>
{
new Student {FirstName = "Ram", LastName = "Kumar", ID = 1,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 90, 81, 81, 80}},
new Student {FirstName = "Amara", LastName = "Mishra", ID = 2,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 100, 87, 91, 93}},
new Student {FirstName = "Amartya", LastName = "Tiwari", ID = 3,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 94, 50, 80, 89}},
new Student {FirstName = "Ambaka", LastName = "Chaurasiya", ID = 4,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 98, 89, 86, 82}},
new Student {FirstName = "Alankrti", LastName = "Yadav", ID = 5,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 30, 71, 91, 71}},
new Student {FirstName = "Amaranayagan", LastName = "Gupta", ID = 6,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 92, 90, 86, 78}},
new Student {FirstName = "Amratav", LastName = "Prasad", ID = 7,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 88, 94, 65, 91}},
new Student {FirstName = "Arbhata", LastName = "Macho", ID = 8,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 75, 84, 20, 39}},
new Student {FirstName = "Arghya", LastName = "Thakur", ID = 9,
Year = GradeLevel.SecondYear,
ExamScores = new List<int>{ 97, 92, 80, 60}},
new Student {FirstName = "Apurva", LastName = "Verma", ID = 10,
Year = GradeLevel.ThirdYear,
ExamScores = new List<int>{ 68, 80, 88, 92}},
new Student {FirstName = "Arib", LastName = "kumar", ID = 11,
Year = GradeLevel.FirstYear,
ExamScores = new List<int>{ 55, 92, 93, 90}},
new Student {FirstName = "Arjuna", LastName = "Singh", ID = 12,
Year = GradeLevel.FourthYear,
ExamScores = new List<int>{ 90, 10, 90, 40}}
};
// used in GroupByRange.
protected static int GetPercentile(Student s)
{
double avg = s.ExamScores.Average();
return avg > 0 ? (int)avg / 10 : 0;
}
//GroupByRange.
public void QueryHighScores(int exam, int score)
{
var highScores = from student in students
where student.ExamScores[exam] > score
select new { Name = student.FirstName, Score = student.ExamScores[exam] };
foreach (var item in highScores)
{
Console.WriteLine(string.Format("{0,-15}{1}", item.Name, item.Score));
}
}
//GroupBySingleProperty().
public void GroupBySingleProperty()
{
Console.WriteLine("Group by a single property in an object:");
var queryLastNames =
from student in students
group student by student.LastName into newGroup
orderby newGroup.Key
select newGroup;
foreach (var nameGroup in queryLastNames)
{
Console.WriteLine(string.Format("Key: {0}"), nameGroup.Key);
foreach (var student in nameGroup)
{
Console.WriteLine(string.Format("\t{0}, {1}"), student.LastName, student.FirstName);
}
}
}
//GroupBySubstring().
public void GroupBySubstring()
{
Console.WriteLine("\r\nGroup by something other than a property of the object:");
var queryFirstLetters =
from student in students
group student by student.LastName[0];
foreach (var studentGroup in queryFirstLetters)
{
Console.WriteLine(string.Format("Key: {0}"), studentGroup.Key);
// Nested foreach is required to access group items.
foreach (var student in studentGroup)
{
Console.WriteLine(string.Format("\t{0}, {1}"), student.LastName, student.FirstName);
}
}
}
//GroupByBoolean()
public void GroupByBoolean()
{
Console.WriteLine("\r\nGroup by a Boolean into two groups with string keys");
Console.WriteLine("\"True\" and \"False\" and project into a new anonymous type:");
var queryGroupByAverages = from student in students
group new { student.FirstName, student.LastName }
by student.ExamScores.Average() > 76 into studentGroup
select studentGroup;
foreach (var studentGroup in queryGroupByAverages)
{
Console.WriteLine(string.Format("Key: {0}"), studentGroup.Key);
foreach (var student in studentGroup)
Console.WriteLine(string.Format("\t{0} {1}"), student.FirstName, student.LastName);
}
}
//GroupByCompositeKey().
public void GroupByCompositeKey()
{
var queryHighScoreGroups =
from student in students
group student by new
{
FirstLetter = student.LastName[0],
Score = student.ExamScores[0] > 86
} into studentGroup
orderby studentGroup.Key.FirstLetter
select studentGroup;
Console.WriteLine("\r\nGroup and order by a compound key:");
foreach (var scoreGroup in queryHighScoreGroups)
{
string s = scoreGroup.Key.Score == true ? "more than" : "less than";
Console.WriteLine(string.Format("Name starts with {0} who scored {s} 86"), scoreGroup.Key.FirstLetter);
foreach (var item in scoreGroup)
{
Console.WriteLine(string.Format("\t{0} {1}", item.FirstName, item.LastName));
}
}
}
//GroupByRange().
public void GroupByRange()
{
Console.WriteLine("\r\nGroup by numeric range and project into a new anonymous type:");
var queryNumericRange =
from student in students
let percentile = GetPercentile(student)
group new { student.FirstName, student.LastName } by percentile into percentGroup
orderby percentGroup.Key
select percentGroup;
foreach (var studentGroup in queryNumericRange)
{
Console.WriteLine(string.Format("Key: {0 * 10}"), studentGroup.Key);
foreach (var item in studentGroup)
{
Console.WriteLine(string.Format("\t{0}, {1}"), item.LastName, item.FirstName);
}
}
}
}
}
}
In this post, How to use group by query in LINQ c#. The GroupBy operator returns a group of elements from the given collection based on some key value. Each group is represented by IGrouping<TKey, TElement> object. Group by query in LINQ in c#
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