我正在寻找一种非常快速的方法来过滤C#中的集合.我目前正在使用通用的List
目前,我只是创建一个新的List
有一个更好的方法吗？有没有办法过滤到位,所以不需要临时列表？
如果你正在使用C#3.0,你可以使用linq,更好的方式和更优雅的方式:
ListmyList = GetListOfIntsFromSomewhere(); // This will filter out the list of ints that are > than 7, Where returns an // IEnumerable so a call to ToList is required to convert back to a List . List filteredList = myList.Where( x => x > 7).ToList();
如果找不到.Where,则意味着您需要using System.Linq;在文件顶部导入.
下面是使用三种不同方法进行列表过滤的代码块/示例,我将它们放在一起以显示Lambdas和基于LINQ的列表过滤.
#region List Filtering
static void Main(string[] args)
{
ListFiltering();
Console.ReadLine();
}
private static void ListFiltering()
{
var PersonList = new List();
PersonList.Add(new Person() { Age = 23, Name = "Jon", Gender = "M" }); //Non-Constructor Object Property Initialization
PersonList.Add(new Person() { Age = 24, Name = "Jack", Gender = "M" });
PersonList.Add(new Person() { Age = 29, Name = "Billy", Gender = "M" });
PersonList.Add(new Person() { Age = 33, Name = "Bob", Gender = "M" });
PersonList.Add(new Person() { Age = 45, Name = "Frank", Gender = "M" });
PersonList.Add(new Person() { Age = 24, Name = "Anna", Gender = "F" });
PersonList.Add(new Person() { Age = 29, Name = "Sue", Gender = "F" });
PersonList.Add(new Person() { Age = 35, Name = "Sally", Gender = "F" });
PersonList.Add(new Person() { Age = 36, Name = "Jane", Gender = "F" });
PersonList.Add(new Person() { Age = 42, Name = "Jill", Gender = "F" });
//Logic: Show me all males that are less than 30 years old.
Console.WriteLine("");
//Iterative Method
Console.WriteLine("List Filter Normal Way:");
foreach (var p in PersonList)
if (p.Gender == "M" && p.Age < 30)
Console.WriteLine(p.Name + " is " + p.Age);
Console.WriteLine("");
//Lambda Filter Method
Console.WriteLine("List Filter Lambda Way");
foreach (var p in PersonList.Where(p => (p.Gender == "M" && p.Age < 30))) //.Where is an extension method
Console.WriteLine(p.Name + " is " + p.Age);
Console.WriteLine("");
//LINQ Query Method
Console.WriteLine("List Filter LINQ Way:");
foreach (var v in from p in PersonList
where p.Gender == "M" && p.Age < 30
select new { p.Name, p.Age })
Console.WriteLine(v.Name + " is " + v.Age);
}
private class Person
{
public Person() { }
public int Age { get; set; }
public string Name { get; set; }
public string Gender { get; set; }
}
#endregion
List具有FindAll方法,它将为您进行过滤并返回列表的子集.
msdn在这里有一个很好的代码示例:http://msdn.microsoft.com/en-us/library/aa701359(VS.80).aspx
编辑:在我对Linq和Where()方法有很好的理解之前,我写过这篇文章.如果我今天写这个,我可能会使用Jorge提到的方法.如果您陷入.NET 2.0环境,FindAll方法仍然有效.
您可以使用IEnumerable来消除临时列表的需要.
public IEnumerableGetFilteredItems(IEnumerable collection) { foreach (T item in collection) if (Matches (item)) { yield return item; } }
其中Matches是过滤方法的名称.你可以这样使用:
IEnumerablefilteredItems = GetFilteredItems(myList); foreach (MyType item in filteredItems) { // do sth with your filtered items }
这将在需要时调用GetFilteredItems函数,并且在某些情况下,您不使用过滤集合中的所有项目,它可以提供一些良好的性能增益.
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