我想知道，RemoveAll和Except之间是否有任何区别，以及使用HashSet的优点，所以我已经做了快速性能检查:)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;

namespace ListRemoveTest
{
    class Program
    {
        private static Random random = new Random( (int)DateTime.Now.Ticks );

        static void Main( string[] args )
        {
            Console.WriteLine( "Be patient, generating data..." );

            List<string> list = new List<string>();
            List<string> toRemove = new List<string>();
            for( int x=0; x < 1000000; x++ )
            {
                string randString = RandomString( random.Next( 100 ) );
                list.Add( randString );
                if( random.Next( 1000 ) == 0 )
                    toRemove.Insert( 0, randString );
            }

            List<string> l1 = new List<string>( list );
            List<string> l2 = new List<string>( list );
            List<string> l3 = new List<string>( list );
            List<string> l4 = new List<string>( list );

            Console.WriteLine( "Be patient, testing..." );

            Stopwatch sw1 = Stopwatch.StartNew();
            l1.RemoveAll( toRemove.Contains );
            sw1.Stop();

            Stopwatch sw2 = Stopwatch.StartNew();
            l2.RemoveAll( new HashSet<string>( toRemove ).Contains );
            sw2.Stop();

            Stopwatch sw3 = Stopwatch.StartNew();
            l3 = l3.Except( toRemove ).ToList();
            sw3.Stop();

            Stopwatch sw4 = Stopwatch.StartNew();
            l4 = l4.Except( new HashSet<string>( toRemove ) ).ToList();
            sw3.Stop();


            Console.WriteLine( "L1.Len = {0}, Time taken: {1}ms", l1.Count, sw1.Elapsed.TotalMilliseconds );
            Console.WriteLine( "L2.Len = {0}, Time taken: {1}ms", l1.Count, sw2.Elapsed.TotalMilliseconds );
            Console.WriteLine( "L3.Len = {0}, Time taken: {1}ms", l1.Count, sw3.Elapsed.TotalMilliseconds );
            Console.WriteLine( "L4.Len = {0}, Time taken: {1}ms", l1.Count, sw3.Elapsed.TotalMilliseconds );

            Console.ReadKey();
        }


        private static string RandomString( int size )
        {
            StringBuilder builder = new StringBuilder();
            char ch;
            for( int i = 0; i < size; i++ )
            {
                ch = Convert.ToChar( Convert.ToInt32( Math.Floor( 26 * random.NextDouble() + 65 ) ) );
                builder.Append( ch );
            }

            return builder.ToString();
        }
    }
}

结果如下:

Be patient, generating data...
Be patient, testing...
L1.Len = 985263, Time taken: 13411.8648ms
L2.Len = 985263, Time taken: 76.4042ms
L3.Len = 985263, Time taken: 340.6933ms
L4.Len = 985263, Time taken: 340.6933ms

如我们所见，这种情况下最好的选择是使用RemoveAll(HashSet)

嗯，从一开始就把他们排除在外会更容易:

authorsList = authorsList.Where(x => x.FirstName != "Bob").ToList();

但是，这只会改变authorsList的值，而不是从以前的集合中删除author。或者，你可以使用RemoveAll:

authorsList.RemoveAll(x => x.FirstName == "Bob");

如果你真的需要基于另一个集合来做，我会使用HashSet, RemoveAll和Contains:

var setToRemove = new HashSet<Author>(authors);
authorsList.RemoveAll(x => setToRemove.Contains(x));

你可以用两种方法去除

var output = from x in authorsList
             where x.firstname != "Bob"
             select x;

or

var authors = from x in authorsList
              where x.firstname == "Bob"
              select x;

var output = from x in authorsList
             where !authors.Contains(x) 
             select x;

我也有同样的问题，如果你想根据你的where条件简单输出，那么第一个解决方案更好。

使用标准LINQ操作符无法做到这一点，因为LINQ提供的是查询，而不是更新支持。

但是您可以生成一个新的列表并替换旧的列表。

var authorsList = GetAuthorList();

authorsList = authorsList.Where(a => a.FirstName != "Bob").ToList();

或者您可以在第二次操作中删除authors中的所有项。

var authorsList = GetAuthorList();

var authors = authorsList.Where(a => a.FirstName == "Bob").ToList();

foreach (var author in authors)
{
    authorList.Remove(author);
}

假设authorsToRemove是一个IEnumerable<T>，其中包含您想从authorsList中删除的元素。

下面是另一种非常简单的方法来完成OP要求的移除任务:

authorsList.RemoveAll(authorsToRemove.Contains);

最好使用List<T>。RemoveAll来完成这个任务。

authorsList.RemoveAll((x) => x.firstname == "Bob");