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.NET: Language Integrated Query (LINQ) - Page 4
Group Clause, GroupBy.
The group Clause
The group clause can be used to group results based on a key.
using System;
using System.Collections.Generic;
using System.Linq;
namespace LinqExample
{
[Serializable]
public class Person : IComparable<Person>, IFormattable
{
public string LastName { get; set; }
public string FirstName { get; set; }
public string Country { get; set; }
public Person(string LastName = null, string FirstName = null, string Country = null)
{
this.LastName = LastName;
this.FirstName = FirstName;
this.Country = Country;
}
public int CompareTo(Person person)
{
if (person == null)
throw new ArgumentNullException("person");
return LastName.CompareTo(person.LastName);
}
public override string ToString()
{
return LastName + ", " + FirstName;
}
public string ToString(string format)
{
return ToString(format, null);
}
public string ToString(string format, IFormatProvider FormatProvider)
{
switch (format)
{
case null:
case "N": // return full name
return ToString();
case "L": // return last name
return LastName;
case "F": // return first name
return FirstName;
case "A": // return all information
return ToString() + " - " + Country.ToString();
default:
throw new FormatException("Format " + format + " unsupported");
}
}
}
public static class Classroom
{
private static List<Person> students;
public static IList<Person> GetAttendance()
{
if (students == null)
{
students = new List<Person>();
students.Add(new Person("Holman", "Kaylee", "Holland"));
students.Add(new Person("Crabtree", "Glenn", "France"));
students.Add(new Person("Kellerman", "Calandra", "United States"));
students.Add(new Person("Chairez", "Judy", "France"));
students.Add(new Person("Santore", "Cari", "Germany"));
students.Add(new Person("Barnaby", "Emelda", "Germany"));
students.Add(new Person("Beeler", "Rufina", "Britain"));
students.Add(new Person("Barreiro", "Jessia", "United States"));
students.Add(new Person("Kummer", "Bebe", "Brazil"));
students.Add(new Person("Sexson", "Aleida", "Italy"));
students.Add(new Person("Ansell", "Freida", "United States"));
students.Add(new Person("Eriksson", "Jae", "Belgium"));
}
return students;
}
}
class Program
{
static void Main()
{
var query = from p in Classroom.GetAttendance()
group p by p.Country into g
orderby g.Count() descending
where g.Count() > 1
select new
{
Country = g.Key,
Count = g.Count()
};
foreach (var obj in query)
{
Console.WriteLine("{0, -15} {1}", obj.Country, obj.Count);
}
}
}
}
United States 3 France 2 Germany 2
Using Lambda with LINQ Methods GroupBy(), OrderByDescending(), Where(), Count() and Select()
using System;
using System.Collections.Generic;
using System.Linq;
namespace LinqExample
{
[Serializable]
public class Person : IComparable<Person>, IFormattable
{
public string LastName { get; set; }
public string FirstName { get; set; }
public string Country { get; set; }
public Person(string LastName = null, string FirstName = null, string Country = null)
{
this.LastName = LastName;
this.FirstName = FirstName;
this.Country = Country;
}
public int CompareTo(Person person)
{
if (person == null)
throw new ArgumentNullException("person");
return LastName.CompareTo(person.LastName);
}
public override string ToString()
{
return LastName + ", " + FirstName;
}
public string ToString(string format)
{
return ToString(format, null);
}
public string ToString(string format, IFormatProvider FormatProvider)
{
switch (format)
{
case null:
case "N": // return full name
return ToString();
case "L": // return last name
return LastName;
case "F": // return first name
return FirstName;
case "A": // return all information
return ToString() + " - " + Country.ToString();
default:
throw new FormatException("Format " + format + " unsupported");
}
}
}
public static class Classroom
{
private static List<Person> students;
public static IList<Person> GetAttendance()
{
if (students == null)
{
students = new List<Person>();
students.Add(new Person("Holman", "Kaylee", "Holland"));
students.Add(new Person("Crabtree", "Glenn", "France"));
students.Add(new Person("Kellerman", "Calandra", "United States"));
students.Add(new Person("Chairez", "Judy", "France"));
students.Add(new Person("Santore", "Cari", "Germany"));
students.Add(new Person("Barnaby", "Emelda", "Germany"));
students.Add(new Person("Beeler", "Rufina", "Britain"));
students.Add(new Person("Barreiro", "Jessia", "United States"));
students.Add(new Person("Kummer", "Bebe", "Brazil"));
students.Add(new Person("Sexson", "Aleida", "Italy"));
students.Add(new Person("Ansell", "Freida", "United States"));
students.Add(new Person("Eriksson", "Jae", "Belgium"));
}
return students;
}
}
class Program
{
static void Main()
{
var query = Classroom.GetAttendance().GroupBy(p => p.Country).OrderByDescending(g => g.Count()).Where(g => g.Count() > 1).Select(g => new { Country = g.Key, Count = g.Count() });
foreach (var obj in query)
{
Console.WriteLine("{0, -15} {1}", obj.Country, obj.Count);
}
}
}
}
Nested Objects
When the grouped object contains nested sequences, just modify the select clause.
using System;
using System.Collections.Generic;
using System.Linq;
namespace LinqExample
{
[Serializable]
public class Person : IComparable<Person>, IFormattable
{
public string LastName { get; set; }
public string FirstName { get; set; }
public string Country { get; set; }
public Person(string LastName = null, string FirstName = null, string Country = null)
{
this.LastName = LastName;
this.FirstName = FirstName;
this.Country = Country;
}
public int CompareTo(Person person)
{
if (person == null)
throw new ArgumentNullException("person");
return LastName.CompareTo(person.LastName);
}
public override string ToString()
{
return LastName + ", " + FirstName;
}
public string ToString(string format)
{
return ToString(format, null);
}
public string ToString(string format, IFormatProvider FormatProvider)
{
switch (format)
{
case null:
case "N": // return full name
return ToString();
case "L": // return last name
return LastName;
case "F": // return first name
return FirstName;
case "A": // return all information
return ToString() + " - " + Country.ToString();
default:
throw new FormatException("Format " + format + " unsupported");
}
}
}
public static class Classroom
{
private static List<Person> students;
public static IList<Person> GetAttendance()
{
if (students == null)
{
students = new List<Person>();
students.Add(new Person("Holman", "Kaylee", "Holland"));
students.Add(new Person("Crabtree", "Glenn", "France"));
students.Add(new Person("Kellerman", "Calandra", "United States"));
students.Add(new Person("Chairez", "Judy", "France"));
students.Add(new Person("Santore", "Cari", "Germany"));
students.Add(new Person("Barnaby", "Emelda", "Germany"));
students.Add(new Person("Beeler", "Rufina", "Britain"));
students.Add(new Person("Barreiro", "Jessia", "United States"));
students.Add(new Person("Kummer", "Bebe", "Brazil"));
students.Add(new Person("Sexson", "Aleida", "Italy"));
students.Add(new Person("Ansell", "Freida", "United States"));
students.Add(new Person("Eriksson", "Jae", "Belgium"));
}
return students;
}
}
class Program
{
static void Main()
{
var query = from p in Classroom.GetAttendance()
group p by p.Country into g
orderby g.Count() descending
where g.Count() > 1
select new
{
Country = g.Key,
Count = g.Count(),
Students = from p2 in g
orderby p2.LastName
select p2.LastName + ", " + p2.FirstName
};
foreach (var obj in query)
{
Console.WriteLine("{0, -15} {1}", obj.Country, obj.Count);
foreach (string s in obj.Students)
{
Console.WriteLine("\t" + s);
}
}
}
}
}
United States 3
Ansell, Freida
Barreiro, Jessia
Kellerman, Calandra
France 2
Chairez, Judy
Crabtree, Glenn
Germany 2
Barnaby, Emelda
Santore, Cari
With LINQ Methods GroupBy(), OrderByDescending(), Where() and Select()
using System;
using System.Collections.Generic;
using System.Linq;
namespace LinqExample
{
[Serializable]
public class Person : IComparable<Person>, IFormattable
{
public string LastName { get; set; }
public string FirstName { get; set; }
public string Country { get; set; }
public Person(string LastName = null, string FirstName = null, string Country = null)
{
this.LastName = LastName;
this.FirstName = FirstName;
this.Country = Country;
}
public int CompareTo(Person person)
{
if (person == null)
throw new ArgumentNullException("person");
return LastName.CompareTo(person.LastName);
}
public override string ToString()
{
return LastName + ", " + FirstName;
}
public string ToString(string format)
{
return ToString(format, null);
}
public string ToString(string format, IFormatProvider FormatProvider)
{
switch (format)
{
case null:
case "N": // return full name
return ToString();
case "L": // return last name
return LastName;
case "F": // return first name
return FirstName;
case "A": // return all information
return ToString() + " - " + Country.ToString();
default:
throw new FormatException("Format " + format + " unsupported");
}
}
}
public static class Classroom
{
private static List<Person> students;
public static IList<Person> GetAttendance()
{
if (students == null)
{
students = new List<Person>();
students.Add(new Person("Holman", "Kaylee", "Holland"));
students.Add(new Person("Crabtree", "Glenn", "France"));
students.Add(new Person("Kellerman", "Calandra", "United States"));
students.Add(new Person("Chairez", "Judy", "France"));
students.Add(new Person("Santore", "Cari", "Germany"));
students.Add(new Person("Barnaby", "Emelda", "Germany"));
students.Add(new Person("Beeler", "Rufina", "Britain"));
students.Add(new Person("Barreiro", "Jessia", "United States"));
students.Add(new Person("Kummer", "Bebe", "Brazil"));
students.Add(new Person("Sexson", "Aleida", "Italy"));
students.Add(new Person("Ansell", "Freida", "United States"));
students.Add(new Person("Eriksson", "Jae", "Belgium"));
}
return students;
}
}
class Program
{
static void Main()
{
var query = Classroom.GetAttendance()
.GroupBy(p => p.Country)
.OrderByDescending(g => g.Count())
.Where(g => g.Count() > 1)
.Select(g => new { Country = g.Key, Count = g.Count(), Students = g.OrderBy(g => g.LastName).Select(s => s.LastName + ", " + s.FirstName) });
foreach (var obj in query)
{
Console.WriteLine("{0, -15} {1}", obj.Country, obj.Count);
foreach (string s in obj.Students)
{
Console.WriteLine("\t" + s);
}
}
}
}
}
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