Some Common GroupBy Operations on List<> using LINQ
The ‘GroupBy’ feature in LINQ is amazing and very powerful. When you use a ‘GroupBy’ in LINQ, internally it calls an extension method which returns a sequence of System.Collections.Generic.IEnumerable<(Of <(IGrouping<(Of <(TKey, TSource>)>)>)>)
The GroupBy<(Of <(TSource, TKey>)>)(IEnumerable<(Of <(TSource>)>), Func<(Of <(TSource, TKey>)>)) method returns a collection of IGrouping<(Of <(TKey, TElement>)>) objects, one for each distinct key that was encountered. The key represents the attribute that is common to each value in the IGrouping<(Of <(TKey, TElement>)>) and can be accessed using a ForEach loop.
In order to understand GroupBy in LINQ, let’s take an example. Linda is an HR in a small private firm. To facilitate the HR process, she wants a simple console application to obtain some quick results. She needs the following details of Employees:
- Raw List of Employees
- List of Employees grouped by the first letter of their FirstName
- List of employees grouped by the Year in which they were born
- List of employees grouped by the Year and Month in which they were born
- Total count of employees having Birthdays in the same Year
- Sex Ratio
Let’s take these requirements one by one and see how they can be easily achieved using the ‘GroupBy’ in LINQ. We will first create a simple list of employees (List<Employees>) and add some data to it.
C#
class Program
{
static void Main(string[] args)
{
List<Employee> empList = new List<Employee>();
empList.Add(new Employee() { ID = 1, FName = "John", MName = "", LName = "Shields", DOB = DateTime.Parse("12/11/1971"), Sex = 'M' });
empList.Add(new Employee() { ID = 2, FName = "Mary", MName = "Matthew", LName = "Jacobs", DOB = DateTime.Parse("01/17/1961"), Sex = 'F' });
empList.Add(new Employee() { ID = 3, FName = "Amber", MName = "Carl", LName = "Agar", DOB = DateTime.Parse("12/23/1971"), Sex = 'M' });
empList.Add(new Employee() { ID = 4, FName = "Kathy", MName = "", LName = "Berry", DOB = DateTime.Parse("11/15/1976"), Sex = 'F' });
empList.Add(new Employee() { ID = 5, FName = "Lena", MName = "Ashco", LName = "Bilton", DOB = DateTime.Parse("05/11/1978"), Sex = 'F' });
empList.Add(new Employee() { ID = 6, FName = "Susanne", MName = "", LName = "Buck", DOB = DateTime.Parse("03/7/1965"), Sex = 'F' });
empList.Add(new Employee() { ID = 7, FName = "Jim", MName = "", LName = "Brown", DOB = DateTime.Parse("09/11/1972"), Sex = 'M' });
empList.Add(new Employee() { ID = 8, FName = "Jane", MName = "G", LName = "Hooks", DOB = DateTime.Parse("12/11/1972"), Sex = 'F' });
empList.Add(new Employee() { ID = 9, FName = "Robert", MName = "", LName = "", DOB = DateTime.Parse("06/28/1964"), Sex = 'M' });
empList.Add(new Employee() { ID = 10, FName = "Cindy", MName = "Preston", LName = "Fox", DOB = DateTime.Parse("01/11/1978"), Sex = 'M' });
// Printing the List
Console.WriteLine("\n{0,2} {1,7} {2,8} {3,8} {4,23} {5,3}",
"ID", "FName", "MName", "LName", "DOB", "Sex");
empList.ForEach(delegate(Employee e)
{
Console.WriteLine("{0,2} {1,7} {2,8} {3,8} {4,23} {5,3}",
e.ID, e.FName, e.MName, e.LName, e.DOB, e.Sex);
});
Console.ReadLine();
}
class Employee
{
public int ID { get; set; }
public string FName { get; set; }
public string MName { get; set; }
public string LName { get; set; }
public DateTime DOB { get; set; }
public char Sex { get; set; }
}
VB.NET
Module Module1
Sub Main()
Dim empList As New List(Of Employee)()
empList.Add(New Employee() With {.ID = 1, .FName = "John", .MName = "", .LName = "Shields", .DOB = DateTime.Parse("12/11/1971"), .Sex = "M"c})
empList.Add(New Employee() With {.ID = 2, .FName = "Mary", .MName = "Matthew", .LName = "Jacobs", .DOB = DateTime.Parse("01/17/1961"), .Sex = "F"c})
empList.Add(New Employee() With {.ID = 3, .FName = "Amber", .MName = "Carl", .LName = "Agar", .DOB = DateTime.Parse("12/23/1971"), .Sex = "M"c})
empList.Add(New Employee() With {.ID = 4, .FName = "Kathy", .MName = "", .LName = "Berry", .DOB = DateTime.Parse("11/15/1976"), .Sex = "F"c})
empList.Add(New Employee() With {.ID = 5, .FName = "Lena", .MName = "Ashco", .LName = "Bilton", .DOB = DateTime.Parse("05/11/1978"), .Sex = "F"c})
empList.Add(New Employee() With {.ID = 6, .FName = "Susanne", .MName = "", .LName = "Buck", .DOB = DateTime.Parse("03/7/1965"), .Sex = "F"c})
empList.Add(New Employee() With {.ID = 7, .FName = "Jim", .MName = "", .LName = "Brown", .DOB = DateTime.Parse("09/11/1972"), .Sex = "M"c})
empList.Add(New Employee() With {.ID = 8, .FName = "Jane", .MName = "G", .LName = "Hooks", .DOB = DateTime.Parse("12/11/1972"), .Sex = "F"c})
empList.Add(New Employee() With {.ID = 9, .FName = "Robert", .MName = "", .LName = "", .DOB = DateTime.Parse("06/28/1964"), .Sex = "M"c})
empList.Add(New Employee() With {.ID = 10, .FName = "Cindy", .MName = "Preston", .LName = "Fox", .DOB = DateTime.Parse("01/11/1978"), .Sex = "M"c})
' Printing the List
Console.WriteLine(Constants.vbLf & "{0,2} {1,7} {2,8} {3,8} {4,23} {5,3}", "ID", "FName", "MName", "LName", "DOB", "Sex")
empList.ForEach(AddressOf AnonymousMethod1)
Console.ReadLine()
End Sub
Private Sub AnonymousMethod1(ByVal e As Employee)
Console.WriteLine("{0,2} {1,7} {2,8} {3,8} {4,23} {5,3}", e.ID, e.FName, e.MName, e.LName, e.DOB, e.Sex)
End Sub
End Module
Friend Class Employee
Private privateID As Integer
Public Property ID() As Integer
Get
Return privateID
End Get
Set(ByVal value As Integer)
privateID = value
End Set
End Property
Private privateFName As String
Public Property FName() As String
Get
Return privateFName
End Get
Set(ByVal value As String)
privateFName = value
End Set
End Property
Private privateMName As String
Public Property MName() As String
Get
Return privateMName
End Get
Set(ByVal value As String)
privateMName = value
End Set
End Property
Private privateLName As String
Public Property LName() As String
Get
Return privateLName
End Get
Set(ByVal value As String)
privateLName = value
End Set
End Property
Private privateDOB As DateTime
Public Property DOB() As DateTime
Get
Return privateDOB
End Get
Set(ByVal value As DateTime)
privateDOB = value
End Set
End Property
Private privateSex As Char
Public Property Sex() As Char
Get
Return privateSex
End Get
Set(ByVal value As Char)
privateSex = value
End Set
End Property
End Class
1. List of Employees grouped by the first letter of their FirstName
To display a list of employees group by the first alphabet of their FirstName, use this query
C#
// Group People by the First Letter of their FirstName
var grpOrderedFirstLetter = empList.GroupBy(employees =>
new String(employees.FName[0], 1)).OrderBy(employees => employees.Key.ToString());;
foreach (var employee in grpOrderedFirstLetter)
{
Console.WriteLine("\n'Employees having First Letter {0}':", employee.Key.ToString());
foreach (var empl in employee)
{
Console.WriteLine(empl.FName);
}
}
Console.ReadLine();
VB.NET
' Group People by the First Letter of their FirstName
Dim grpOrderedFirstLetter = empList.GroupBy(Function(employees) New String(employees.FName(0), 1)).OrderBy(Function(employees) employees.Key.ToString())
For Each employee In grpOrderedFirstLetter
Console.WriteLine(Constants.vbLf & "'Employees having First Letter {0}':", employee.Key.ToString())
For Each empl In employee
Console.WriteLine(empl.FName)
Next empl
Next employee
Console.ReadLine()
2. List of Employees grouped by the Year in which they were Born
In order to group the employees based on the year in which they were born, use this query
C#
// Group People by the Year in which they were born
var grpOrderedYr = empList.GroupBy(employees => employees.DOB.Year).OrderBy(employees => employees.Key);
foreach (var employee in grpOrderedYr)
{
Console.WriteLine("\nEmployees Born In the Year " + employee.Key);
foreach (var empl in employee)
{
Console.WriteLine("{0,2} {1,7}", empl.ID, empl.FName);
}
}
Console.ReadLine();
VB.NET
' Group People by the Year in which they were born
Dim grpOrderedYr = empList.GroupBy(Function(employees) employees.DOB.Year).OrderBy(Function(employees) employees.Key)
For Each employee In grpOrderedYr
Console.WriteLine(Constants.vbLf & "Employees Born In the Year " & employee.Key)
For Each empl In employee
Console.WriteLine("{0,2} {1,7}", empl.ID, empl.FName)
Next empl
Next employee
Console.ReadLine()
3. List of employees grouped by the Year and Month in which they were born
In order to group the employees based on the year and then the month in which they were born, use this query
C#
// Group people by the Year and Month in which they were born
var grpOrderedYrMon = empList.GroupBy(employees =>
new DateTime(employees.DOB.Year, employees.DOB.Month, 1)).OrderBy(employees => employees.Key); ;
foreach (var employee in grpOrderedYrMon)
{
Console.WriteLine("\nEmployees Born in Year {0} - Month {1} is/are :", employee.Key.Year, employee.Key.Month);
foreach (var empl in employee)
{
Console.WriteLine("{0}: {1}", empl.ID, empl.FName);
}
}
Console.ReadLine();
VB.NET
' Group people by the Year and Month in which they were born
Dim grpOrderedYrMon = empList.GroupBy(Function(employees) New DateTime(employees.DOB.Year, employees.DOB.Month, 1)).OrderBy(Function(employees) employees.Key)
For Each employee In grpOrderedYrMon
Console.WriteLine(Constants.vbLf & "Employees Born in Year {0} - Month {1} is/are :", employee.Key.Year, employee.Key.Month)
For Each empl In employee
Console.WriteLine("{0}: {1}", empl.ID, empl.FName)
Next empl
Next employee
Console.ReadLine()
4. Total No. Of Birthdays each Year
To get a total of the employees born in the same year, use this query
C#
// Count people grouped by the Year in which they were born
var grpCountYrMon = empList.GroupBy(employees => employees.DOB.Year)
.Select(lst => new {Year = lst.Key, Count = lst.Count()} );
foreach (var employee in grpCountYrMon)
{
Console.WriteLine("\n{0} were born in {1}", employee.Count, employee.Year);
}
Console.ReadLine();
VB.NET
' Count people grouped by the Year in which they were born
Dim grpCountYrMon = empList.GroupBy(Function(employees) employees.DOB.Year).Select(Function(lst) New With {Key .Year = lst.Key, Key .Count = lst.Count()})
For Each employee In grpCountYrMon
Console.WriteLine(Constants.vbLf & "{0} were born in {1}", employee.Count, employee.Year)
Next employee
Console.ReadLine()
5. Sex Ratio
To find the sex ratio in the company, use this query
C#
// Sex Ratio
var ratioSex = empList.GroupBy(ra => ra.Sex)
.Select( emp => new
{
Sex = emp.Key,
Ratio = (emp.Count() * 100) / empList.Count
});
foreach (var ratio in ratioSex)
{
Console.WriteLine("\n{0} are {1}%", ratio.Sex, ratio.Ratio);
}
Console.ReadLine();
VB.NET ' Sex Ratio
Dim ratioSex = empList.GroupBy(Function(ra) ra.Sex).Select(Function(emp) New With {Key .Sex = emp.Key, Key .Ratio = (emp.Count() * 100) / empList.Count})
For Each ratio In ratioSex
Console.WriteLine(Constants.vbLf & "{0} are {1}%", ratio.Sex, ratio.Ratio)
Next ratio
Console.ReadLine()
Well I hope you got a fair bit of idea of the power of a GroupBy in LINQ and so did Linda, our fictional HR J. So Happy LINQing and keep practising! I hope you liked the article and I thank you for viewing it. The entire source code of this article in C# and VB.NET can be downloaded over here.
This article has been editorially reviewed by Suprotim Agarwal.
C# and .NET have been around for a very long time, but their constant growth means there’s always more to learn.
We at DotNetCurry are very excited to announce The Absolutely Awesome Book on C# and .NET. This is a 500 pages concise technical eBook available in PDF, ePub (iPad), and Mobi (Kindle).
Organized around concepts, this Book aims to provide a concise, yet solid foundation in C# and .NET, covering C# 6.0, C# 7.0 and .NET Core, with chapters on the latest .NET Core 3.0, .NET Standard and C# 8.0 (final release) too. Use these concepts to deepen your existing knowledge of C# and .NET, to have a solid grasp of the latest in C# and .NET OR to crack your next .NET Interview.
Click here to Explore the Table of Contents or Download Sample Chapters!
Was this article worth reading? Share it with fellow developers too. Thanks!
Suprotim Agarwal, MCSD, MCAD, MCDBA, MCSE, is the founder of
DotNetCurry,
DNC Magazine for Developers,
SQLServerCurry and
DevCurry. He has also authored a couple of books
51 Recipes using jQuery with ASP.NET Controls and
The Absolutely Awesome jQuery CookBook.
Suprotim has received the prestigious Microsoft MVP award for Sixteen consecutive years. In a professional capacity, he is the CEO of A2Z Knowledge Visuals Pvt Ltd, a digital group that offers Digital Marketing and Branding services to businesses, both in a start-up and enterprise environment.
Get in touch with him on Twitter @suprotimagarwal or at LinkedIn