var distinctItems = items.Distinct();

为了只匹配某些属性，可以创建一个自定义的相等比较器，例如:

class DistinctItemComparer : IEqualityComparer<Item> {

    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();
    }
}

然后这样使用它:

var distinctItems = items.Distinct(new DistinctItemComparer());

使用Distinct()，但请记住，它使用默认的相等比较器来比较值，因此如果您想要其他的比较器，则需要实现自己的比较器。

有关示例，请参见http://msdn.microsoft.com/en-us/library/bb348436.aspx。

如果有一些东西在Distinct查询中被抛出，您可能需要查看MoreLinq并使用DistinctBy操作符并根据id选择不同的对象。

var distinct = items.DistinctBy( i => i.Id );

var distinctItems = items.GroupBy(x => x.Id).Select(y => y.First());

这就是我如何能够通过Linq分组。希望能有所帮助。

var query = collection.GroupBy(x => x.title).Select(y => y.FirstOrDefault());

List<Employee> employees = new List<Employee>()
{
    new Employee{Id =1,Name="AAAAA"}
    , new Employee{Id =2,Name="BBBBB"}
    , new Employee{Id =3,Name="AAAAA"}
    , new Employee{Id =4,Name="CCCCC"}
    , new Employee{Id =5,Name="AAAAA"}
};

List<Employee> duplicateEmployees = employees.Except(employees.GroupBy(i => i.Name)
                                             .Select(ss => ss.FirstOrDefault()))
                                            .ToList();

你有三个选项来删除列表中的重复项:

Use a a custom equality comparer and then use Distinct(new DistinctItemComparer()) as @Christian Hayter mentioned. Use GroupBy, but please note in GroupBy you should Group by all of the columns because if you just group by Id it doesn't remove duplicate items always. For example consider the following example: List<Item> a = new List<Item> { new Item {Id = 1, Name = "Item1", Code = "IT00001", Price = 100}, new Item {Id = 2, Name = "Item2", Code = "IT00002", Price = 200}, new Item {Id = 3, Name = "Item3", Code = "IT00003", Price = 150}, new Item {Id = 1, Name = "Item1", Code = "IT00001", Price = 100}, new Item {Id = 3, Name = "Item3", Code = "IT00003", Price = 150}, new Item {Id = 3, Name = "Item3", Code = "IT00004", Price = 250} }; var distinctItems = a.GroupBy(x => x.Id).Select(y => y.First()); The result for this grouping will be: {Id = 1, Name = "Item1", Code = "IT00001", Price = 100} {Id = 2, Name = "Item2", Code = "IT00002", Price = 200} {Id = 3, Name = "Item3", Code = "IT00003", Price = 150} Which is incorrect because it considers {Id = 3, Name = "Item3", Code = "IT00004", Price = 250} as duplicate. So the correct query would be: var distinctItems = a.GroupBy(c => new { c.Id , c.Name , c.Code , c.Price}) .Select(c => c.First()).ToList(); 3.Override Equal and GetHashCode in item class: public class Item { public int Id { get; set; } public string Name { get; set; } public string Code { get; set; } public int Price { get; set; } public override bool Equals(object obj) { if (!(obj is Item)) return false; Item p = (Item)obj; return (p.Id == Id && p.Name == Name && p.Code == Code && p.Price == Price); } public override int GetHashCode() { return String.Format("{0}|{1}|{2}|{3}", Id, Name, Code, Price).GetHashCode(); } } Then you can use it like this: var distinctItems = a.Distinct();

试试这个扩展方法。希望这能有所帮助。

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)));
    }
}

用法:

var outputList = sourceList.DistinctBy(x => x.TargetProperty);

当你不想写IEqualityComparer时，你可以试试下面的方法。

 class Program
{

    private static void Main(string[] args)
    {

        var items = new List<Item>();
        items.Add(new Item {Id = 1, Name = "Item1"});
        items.Add(new Item {Id = 2, Name = "Item2"});
        items.Add(new Item {Id = 3, Name = "Item3"});

        //Duplicate item
        items.Add(new Item {Id = 4, Name = "Item4"});
        //Duplicate item
        items.Add(new Item {Id = 2, Name = "Item2"});

        items.Add(new Item {Id = 3, Name = "Item3"});

        var res = items.Select(i => new {i.Id, i.Name})
            .Distinct().Select(x => new Item {Id = x.Id, Name = x.Name}).ToList();

        // now res contains distinct records
    }



}


public class Item
{
    public int Id { get; set; }

    public string Name { get; set; }
}

一个通用的扩展方法:

public static class EnumerableExtensions
{
    public static IEnumerable<T> DistinctBy<T, TKey>(this IEnumerable<T> enumerable, Func<T, TKey> keySelector)
    {
        return enumerable.GroupBy(keySelector).Select(grp => grp.First());
    }
}

用法示例:

var lstDst = lst.DistinctBy(item => item.Key);

另一种变通方法，不美观买不可行。

我有一个XML文件，其中有一个名为“MEMDES”的元素，具有“GRADE”和“SPD”两个属性，用于记录RAM模块信息。 SPD中有很多重复的项目。

下面是我用来删除重复项的代码:

        IEnumerable<XElement> MList =
            from RAMList in PREF.Descendants("MEMDES")
            where (string)RAMList.Attribute("GRADE") == "DDR4"
            select RAMList;

        List<string> sellist = new List<string>();

        foreach (var MEMList in MList)
        {
            sellist.Add((string)MEMList.Attribute("SPD").Value);
        }

        foreach (string slist in sellist.Distinct())
        {
            comboBox1.Items.Add(slist);
        }