在 C#2.0 中不使用 foreach 循环的 Filter List<> 对象
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Filter List<> object without using foreach loop in C#2.0
提问by Kthevar
How we can filter the object in List<> in C#?
我们如何在 C# 中过滤 List<> 中的对象？
采纳答案by Razzie
Let's say we have a List<string>and you want only the items where the length of the string is greater than 5.
假设我们有 aList<string>并且您只想要字符串长度大于 5 的项目。
The code below will return a List<string>with the results:
下面的代码将返回一个List<string>结果：
List<string> myList = new List<string>();
myList.Add("hello");
myList.Add("world!");
myList.Add("one");
myList.Add("large!!");
List<string> resultList = myList.FindAll(delegate(string s) { return s.Length > 5; });
resultList will containt 'world!' and 'large!!'. This example uses an anonymous method. It can also be written as:
结果列表将包含“世界！” 和“大！！”。此示例使用匿名方法。也可以写成：
List<string> myList = new List<string>();
// ..
List<string> resultList = myList.FindAll(OnlyLargerThanFive);
//..
private static bool OnlyLargerThanFive(string s)
{
return s.Length > 5;
}
The delegate above, OnlyLargerThanFive, is also called a Predicate.
上面的委托 OnlyLargerThanFive 也称为Predicate。
回答by TheVillageIdiot
besides the way told by @Razzieyou can also use LINQ.
List<string> myList = new List<string>();
myList.Add("hello");
myList.Add("world!");
myList.Add("one");
myList.Add("large!!");
var filtered=from s in myList where s.Length > 5 select s;
PS:- IS ONLY POSSIBLE IN .NET 3 and above
PS：-仅在 .NET 3 及以上版本中才有可能
回答by Migol
The best solution is to use lambda:
最好的解决方案是使用 lambda：
List<Item> l;
l.FindAll(n => n.Something == SomethingElse);
It may use internally foreach, but you can't really filter without iterating for whole list.
它可能会在内部使用 foreach，但如果不迭代整个列表，就无法真正进行过滤。
回答by itsmatt
You could use LINQ. I haven't tested this, but I believe it'll filter down the elements of my list of pie fillings to show only those that start with a "P":
你可以使用LINQ。我还没有测试过这个，但我相信它会过滤掉我的馅饼列表中的元素，只显示那些以“P”开头的元素：
List<string> list = new List<string>();
list.Add("Apple");
list.Add("Peach");
list.Add("Chocolate");
list.Add("Pear");
list.Add("Pumpkin");
list.Add("Cherry");
list.Add("Coconut");
var filteredOnes = from item in list
where item.StartsWith("P")
select item;
回答by SO User
List<>.Find (gives the first matching occurence) and List.FindAll() gives all matching occurences. An example with a list of complex types would is as follow:
List<>.Find（给出第一个匹配的出现）和 List.FindAll() 给出所有匹配的出现。具有复杂类型列表的示例如下：
I have a class Report:
我有一个班级报告：
public class Report
{
public string ReportName;
public ReportColumnList ReportColumnList;
}
and a list of Report
和一份报告清单
List<Report> reportList;
To find items in the list where ReportName = 'MyReport', the code would be:
要在列表中查找 ReportName = 'MyReport' 的项目，代码为：
string reportName = "MyReport";
List<Report> myReports = reportList.FindAll(delegate(Report obj) { return obj.ReportName == reportName; });
To get the first report:
获取第一份报告：
Report rc = reportList.Find(delegate(Report obj) { return obj.ReportName == reportName; });
Note that the object passed to the delegate should be of the type with which the list is populated.
请注意，传递给委托的对象应该是填充列表的类型。
回答by Yissachar
You can use LINQlike this.
您可以像这样使用LINQ。
List<string> List = new List<string> { "i", "am", "using", "LINQ!" };List<string> result = myList.Where(s => s.Length > 3).ToList();
List<string> List = new List<string> { "i", "am", "using", "LINQ!" };List<string> result = myList.Where(s => s.Length > 3).ToList();
it's working only in .net 3 and above.
它仅适用于 .net 3 及更高版本。
