【LINQ】 Aggregate的用法

 

msdn Aggregate

 

原文地址：http://www.studyofnet.com/news/1154.html

 

1.Aggregate用于集合的简单的累加、阶乘

using System;
using System.Linq;
 
class Program
{
 static void Main()
 {
 int[] array = { 1, 2, 3, 4, 5 };
 int result = array.Aggregate((a, b) => b + a);
 // 1 + 2 = 3
 // 3 + 3 = 6
 // 6 + 4 = 10
 // 10 + 5 = 15
 Console.WriteLine(result);
 
 result = array.Aggregate((a, b) => b * a);
 // 1 * 2 = 2
 // 2 * 3 = 6
 // 6 * 4 = 24
 // 24 * 5 = 120
 Console.WriteLine(result);
 }
}


//输出结果： 

//15 

//120 

 

2.Aggregate，在字符串中反转单词的排序

string sentence = "the quick brown fox jumps over the lazy dog";

string[] words = sentence.Split(' ');

string reversed = words.Aggregate((workingSentence, next) =>next + " " + workingSentence);

Console.WriteLine(reversed);

//输出结果： 

//dog lazy the over jumps fox brown quick the 

3.使用 Aggregate 应用累加器函数和结果选择器

//下例使用linq的Aggregate方法找出数组中大于"banana", 长度最长的字符串，并把它转换大写。

string[] fruits ={ 
 "apple", "mango", "orange", "passionfruit", "grape" 
};

string longestName = 
  fruits.Aggregate("banana",
     (longest, next) =>
      next.Length > longest.Length ? next : longest,
     fruit => fruit.ToUpper()); 

 Console.WriteLine(
 "The fruit with the longest name is {0}.",longestName);

//输出结果：

//The fruit with the longest name is PASSIONFRUIT. 

4.使用 Aggregate 应用累加器函数和使用种子值

//下例使用linq的Aggregate方法统计一个数组中偶数的个数。

int[] ints = { 4, 8, 8, 3, 9, 0, 7, 8, 2 };
 
//统计一个数组中偶数的个数，种子值设置为0，找到偶数就加1
int numEven = ints.Aggregate(0, (total, next) =>
         next % 2 == 0 ? total + 1 : total);
 
Console.WriteLine("The number of even integers is: {0}", numEven);


//输出结果:

//The number of even integers is: 6