Linq学习笔记--聚合函数/Aggregator
///
/// 去掉重复项之后，获得个数
///
public void Linq1()
{
int[] factorsOf300 = { 2, 2, 3, 5, 5 };
int uniqueFactors = factorsOf300.Distinct().Count();
Console.WriteLine("There are {0} unique factors of 300.", uniqueFactors);
}
---结果 3
///
/// 带有Lambda表达式的、
/// 获得所有的奇数的个数
///
public void Linq2()
{
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
int oddNumbers = numbers.Count(n => n % 2 == 1);
Console.WriteLine("There are {0} odd numbers in the list.", oddNumbers);
}
---结果 5
///
/// 带有Lambda表达式的、
/// 获得所有的奇数的个数
///
public void Linq3()
{
List
var categoryCounts =
from p in products
group p by p.Category into g //按每个对象的"分类"进行分组,并给每个组起名为g(个人理解..)
select new { Category = g.Key, ProductCount = g.Count() };
}
///
/// 求和
///
public void Linq4()
{
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
double numSum = numbers.Sum();
Console.WriteLine("The sum of the numbers is {0}.", numSum);
}
---结果 The sum of the numbers is 45.
///
/// 求:所有字母长度的和
///
public void Linq5()
{
string[] words = { "cherry", "apple", "blueberry" };
double totalChars = words.Sum(w => w.Length);
Console.WriteLine("There are a total of {0} characters in these words.", totalChars);
}
---结果 There are a total of 20 characters in these words.
///
/// 求最小值
///
public void Linq6()
{
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
int minNum = numbers.Min();
Console.WriteLine("The minimum number is {0}.", minNum);
}
---结果 The minimum number is 0.
///
/// 求最短的单词长度
///
public void Linq7()
{
string[] words = { "cherry", "apple", "blueberry" };
int shortestWord = words.Min(w => w.Length);
Console.WriteLine("The shortest word is {0} characters long.", shortestWord);
}
---结果 The shortest word is 5 characters long.
///
/// 求大值
///
public void Linq8()
{
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
int maxNum = numbers.Max();
Console.WriteLine("The maximum number is {0}.", maxNum);
}
---结果 The maximum number is 9.
///
/// 求平均数
///
public void Linq9()
{
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
double averageNum = numbers.Average();
Console.WriteLine("The average number is {0}.", averageNum);
}
---结果 The average number is 4.5.
===============================华丽的分割线===============================
///
/// 累计求乘积
///
public void Linq10()
{
double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 };
//累计的一个循环相乘的过程,返回最后相乘后的结果
double product = doubles.Aggregate((runningProduct, nextFactor) => runningProduct * nextFactor);
Console.WriteLine("Total product of all numbers: {0}", product);
}
---结果 Total product of all numbers: 88.33081
///
/// 我也不知道这个例子是到底要干什么.可能只是为了讲述语法吧...
///
public void Linq11()
{
double startBalance = 100.0;
int[] attemptedWithdrawals = { 20, 10, 40, 50, 10, 70, 30 };
//乍一看有些复杂,让人找不着北,其实慢慢细看,其实也就是Lambda里嵌套一个Lambda,
//我们可以把代码拆分为AAAA() :下面....
double endBalance =
attemptedWithdrawals.Aggregate(startBalance,
(balance, nextWithdrawal) =>
((nextWithdrawal <= balance) ? (balance - nextWithdrawal) : balance));
Console.WriteLine("Ending balance: {0}", endBalance);
}
///
/// 这是上面拆分来的代码~
///
public void AAAA()
{
double startBalance = 100.0;
int[] attemptedWithdrawals = { 20, 10, 40, 50, 10, 70, 30 };
double endBalance =
attemptedWithdrawals.Aggregate(startBalance,(balance, nextWithdrawal) =>aaa(balance,nextWithdrawal));
Console.WriteLine("Ending balance: {0}", endBalance);
}
double aaa(double a, double b)
{
return (b <= a) ? (a - b) : a;
}
---结果 DE>Ending balance: 20DE>
///
/// let关键字的用法。传统的子查询看起来始终有些不太直观
/// 两种写法效果一样，并且let更加直观
/// (个人感觉就像一个给子查询的别名)
///
public void Linq12()
{
int[] numbers = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
//传统下的子查询做法
var query = from num in numbers
select num * (from n in numbers where n % 2 == 0 select n).Count();
//使用LET关键字的做法
//var query = from num in numbers
//let evenNumbers = from n in numbers //给查询出来的能整除2的数字一个"名字"
//where n % 2 == 0
//select n
//select num * evenNumbers.Count();
foreach (var item in query)
{
Console.WriteLine(item);
}
}
---结果
4
8
12
16
20
24
28
32
36