C# Enumerable GroupBy(IEnumerable, Func, Func, TResult>)
Description
Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key.
Syntax
public static IEnumerable<TResult> GroupBy<TSource, TKey, TResult>(
this IEnumerable<TSource> source,
Func<TSource, TKey> keySelector,
Func<TKey, IEnumerable<TSource>, TResult> resultSelector
)/* w ww . java 2s . c o m*/
Parameters
TSource- The type of the elements of source.TKey- The type of the key returned by keySelector.TResult- The type of the result value returned by resultSelector.source- An IEnumerablewhose elements to group. keySelector- A function to extract the key for each element.resultSelector- A function to create a result value from each group.
Example
The following code example demonstrates how to use GroupBy to group the elements of a sequence and project a sequence of results of type TResult.
/* w ww .ja v a2 s. c o m*/
using System;
using System.Linq;
using System.Collections.Generic;
public class MainClass{
public static void Main(String[] argv){
List<Pet> petsList =new List<Pet>{ new Pet { Name="A", Age=8.3 },
new Pet { Name="B", Age=4.9 },
new Pet { Name="C", Age=1.5 },
new Pet { Name="D", Age=4.3 } };
var query = petsList.GroupBy(
pet => Math.Floor(pet.Age),
(age, pets) => new
{
Key = age,
Count = pets.Count(),
Min = pets.Min(pet => pet.Age),
Max = pets.Max(pet => pet.Age)
});
foreach (var result in query)
{
Console.WriteLine("\nAge group: " + result.Key);
Console.WriteLine("Number of pets in this age group: " + result.Count);
Console.WriteLine("Minimum age: " + result.Min);
Console.WriteLine("Maximum age: " + result.Max);
}
}
}
class Pet{
public string Name { get; set; }
public double Age { get; set; }
}
The code above generates the following result.
