Linq中的TakeWhile和SkipWhile
Linq中的TakeWhile和SkipWhileLinq中的SkipWhile
1、含义
(1)、对数据源进行枚举,从第一个枚举得到的元素开始,调用客户端的predicate
(2)、如果返回true,则跳过该元素,继续进行枚举操作.
(3)、但是,如果一旦predicate返回为false,则该元素以后的所有元素,都不会再调用predicate,而全部枚举给客户端.
2、实现
public static IEnumerable<TSource> SkipWhile<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
if (source == null) throw Error.ArgumentNull("source");
if (predicate == null) throw Error.ArgumentNull("predicate");
return SkipWhileIterator<TSource>(source, predicate);
}
private static IEnumerable<TSource> SkipWhileIterator<TSource>(IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
bool iteratorVariable0 = false;
foreach (TSource iteratorVariable1 in source)
{
if (!iteratorVariable0 && !predicate(iteratorVariable1)) iteratorVariable0 = true;
if (iteratorVariable0)
{
yield return iteratorVariable1;
}
}
}
3、实例
int[] grades = { 59, 82, 70, 56, 92, 98, 85 };
IEnumerable<int> lowerGrades =
grades
.OrderByDescending(grade => grade)
.SkipWhile(grade => grade >= 80);
Console.WriteLine("All grades below 80:");
foreach (int grade in lowerGrades)
{
Console.WriteLine(grade);
}
/*
This code produces the following output:
All grades below 80:
70
59
56
*/
二、Linq中的TakeWhile
1、含义
(1)、对数据源进行枚举，从第一个枚举得到的元素开始,调用客户端传入的predicate( c.Name == ""woodyN")
(2)、如果这个predicate委托返回true的话,则将该元素作为Current元素返回给客户端,并且,继续进行相同的枚举,判断操作.
(3)、但是,一旦predicate返回false的话,MoveNext()方法将会返回false,枚举就此打住,忽略剩下的所有元素.
2、实例
string[] fruits = { "apple", "banana", "mango", "orange",
"passionfruit", "grape" };
IEnumerable<string> query =
fruits.TakeWhile(fruit => String.Compare("orange", fruit, true) != 0);
foreach (string fruit in query)
{
Console.WriteLine(fruit);
}
/*
This code produces the following output:
apple
banana
mango
*/
三、通过一个实例说明Linq中的TakeWhile和SkipWhile的区别
static List<Customer> customers = new List<Customer> {
new Customer { CustomerID=1,Name="woody1"},
new Customer { CustomerID=2,Name="woody2"},
new Customer { CustomerID=3,Name="woody3"},
new Customer { CustomerID=4,Name="woody1"}
};
var cs1 = customers.TakeWhile(c => c.Name == "woody1");
var cs2 = customers.TakeWhile(c => c.Name == "woody2");
var cs3 = customers.SkipWhile(c => c.Name == "woody1");
var cs4 = customers.SkipWhile(c => c.Name == "woody2");
cs1--cs4的结果
cs1 : woody1(CustomerID=1)
cs2 : 没有任何元素
cs3 : woody2 , woody3 , woody1(CustomerID=4)
cs4 : woody1(CustomerID=1),woody2,woody3,woody1(CustomerID=4)