.NET[C#]使用LINQ从List集合中删除重复对象元素(去重)的方法有哪些？

问题描述
比如有如下的List集合：

1 Item1 IT00001 $100
2 Item2 IT00002 $200
3 Item3 IT00003 $150
1 Item1 IT00001 $100
3 Item3 IT00003 $150
使用LINQ如何实现对以上List集合的去重操作，具体实现有哪些呢？

方案一
var distinctItems = items.Distinct();
如果需要对泛型实体中的部分属性进行去重操作，则可以创建一个自定义的比较器：

class DistinctItemComparer : IEqualityComparer {

public bool Equals(Item x, Item y) {
    return x.Id == y.Id &&
        x.Name == y.Name &&
        x.Code == y.Code &&
        x.Price == y.Price;
}

public int GetHashCode(Item obj) {
    return obj.Id.GetHashCode() ^
        obj.Name.GetHashCode() ^
        obj.Code.GetHashCode() ^
        obj.Price.GetHashCode();
}

}
调用方法：

var distinctItems = items.Distinct(new DistinctItemComparer());
方案二（推荐）
var distinctItems = items.GroupBy(x => x.Id).Select(y => y.First());
方案三
使用 MoreLinq 组件：

var distinct = items.DistinctBy( i => i.Id );
方案四
var query = collection.GroupBy(x => x.title).Select(y => y.FirstOrDefault());
方案五
创建静态扩展方法，如：

public static class DistinctHelper
{
public static IEnumerable DistinctBy<TSource, TKey>(this IEnumerable source, Func<TSource, TKey> keySelector)
{
var identifiedKeys = new HashSet();
return source.Where(element => identifiedKeys.Add(keySelector(element)));
}
}
调用方法：

var outputList = sourceList.DistinctBy(x => x.TargetProperty);
其中 x.TargetProperty 请替换成类对应的属性。

示例程序：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var people = new List
{
new Person {Id=1,Name=“Curry”,Age=26 },
new Person {Id=1,Name=“Curry”,Age=26 },
new Person {Id=3,Name=“James”,Age=27 },
new Person {Id=4,Name=“Kobe”,Age=38 }
};
var distinctPeople = people.DistinctBy(x => x.Name).ToList();
distinctPeople.ForEach(x =>
Console.WriteLine($“Id:{x.Id},Name:{x.Name},Age:{x.Age}”)
);
Console.ReadKey();
}
}

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

public static class DistinctHelper
{
    public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
    {
        var identifiedKeys = new HashSet<TKey>();
        return source.Where(element => identifiedKeys.Add(keySelector(element)));
    }
}

}
方案六
public static class DistinctHelper
{
public static IEnumerable DistinctBy<TSource, TKey>(this IEnumerable source, Func<TSource, TKey> keySelector)
{
var identifiedKeys = new HashSet();

        foreach (var item in source)
        {
            if (identifiedKeys.Add(keySelector(item)))
                yield return item;
        }
    }
}