.NET: Language Integrated Query (LINQ) - Page 5

The Min() Max() Average() Sum() Operators

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 int Age { get; set; }

		public Person(string LastName = null, string FirstName = null, int Age = 0)
		{
			this.LastName = LastName;
			this.FirstName = FirstName;
			this.Age = Age;
		}
		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() + " - " + Age.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", 35));
				students.Add(new Person("Crabtree", "Glenn", 30));
				students.Add(new Person("Kellerman", "Calandra", 30));
				students.Add(new Person("Chairez", "Judy", 27));
				students.Add(new Person("Santore", "Cari", 42));
				students.Add(new Person("Barnaby", "Emelda", 27));
				students.Add(new Person("Beeler", "Rufina", 22));
				students.Add(new Person("Barreiro", "Jessia", 31));
				students.Add(new Person("Kummer", "Bebe", 30));
				students.Add(new Person("Sexson", "Aleida", 25));
				students.Add(new Person("Ansell", "Freida", 44));
				students.Add(new Person("Eriksson", "Jae", 49));
			}
			return students;
		}
	}

	class Program
	{
		static void Main()
		{
			var minmaxQuery = from p in Classroom.GetAttendance()
								group p by 0 into g
								select new
								{
									Min = (from p2 in g
										 select p2.Age).Min(),
									Max = (from p2 in g
										 select p2.Age).Max(),
									Average = (from p2 in g
											 select p2.Age).Average(),
									Sum = (from p2 in g
											 select p2.Age).Sum(),
								};
			foreach (var obj in minmaxQuery)
			{
				Console.WriteLine("Min: {0}", obj.Min);
				Console.WriteLine("Max: {0}", obj.Max);
				Console.WriteLine("Average: {0:0,0}", obj.Average);
				Console.WriteLine("Sum: {0}", obj.Sum);
			}
		}
	}
}

Min: 22
Max: 49
Average: 33
Sum: 392

Using Lambda with LINQ Methods GroupBy() 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 int Age { get; set; }

		public Person(string LastName = null, string FirstName = null, int Age = 0)
		{
			this.LastName = LastName;
			this.FirstName = FirstName;
			this.Age = Age;
		}
		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() + " - " + Age.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", 35));
				students.Add(new Person("Crabtree", "Glenn", 30));
				students.Add(new Person("Kellerman", "Calandra", 30));
				students.Add(new Person("Chairez", "Judy", 27));
				students.Add(new Person("Santore", "Cari", 42));
				students.Add(new Person("Barnaby", "Emelda", 27));
				students.Add(new Person("Beeler", "Rufina", 22));
				students.Add(new Person("Barreiro", "Jessia", 31));
				students.Add(new Person("Kummer", "Bebe", 30));
				students.Add(new Person("Sexson", "Aleida", 25));
				students.Add(new Person("Ansell", "Freida", 44));
				students.Add(new Person("Eriksson", "Jae", 49));
			}
			return students;
		}
	}

	class Program
	{
		static void Main()
		{
			var minmaxQuery = Classroom.GetAttendance()
						.GroupBy(g => 0)
						.Select(g => new
						{
							Min = g.Select(p => p.Age).Min(),
							Max = g.Select(p => p.Age).Max(),
							Average = g.Select(p => p.Age).Average(),
							Sum = g.Select(p => p.Age).Sum()
						});
			foreach (var obj in minmaxQuery)
			{
				Console.WriteLine("Min: {0}", obj.Min);
				Console.WriteLine("Max: {0}", obj.Max);
				Console.WriteLine("Average: {0:0,0}", obj.Average);
				Console.WriteLine("Sum: {0}", obj.Sum);
			}
		}
	}
}

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