使用linq删除列表中的重复项

Question

我上课Items了properties (Id, Name, Code, Price).

列表中Items填充了重复的项目.

例如:

1         Item1       IT00001        $100
2         Item2       IT00002        $200
3         Item3       IT00003        $150
1         Item1       IT00001        $100
3         Item3       IT00003        $150

如何使用linq删除列表中的重复项？

Answer 1

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

Answer 2

var distinctItems = items.Distinct();

要仅匹配某些属性,请创建自定义相等比较器,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();
    }
}

然后像这样使用它:

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

Answer 3

如果有什么东西会抛弃您的Distinct查询,您可能需要查看MoreLinq并使用DistinctBy运算符并按ID选择不同的对象.

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

Answer 4

这就是我能够与Linq分组的方式.希望能帮助到你.

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

Answer 5

使用Distinct(),但请记住,它使用默认的相等比较器对值进行比较,所以如果你想超出了任何你需要实现自己的比较器.

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

Answer 6

您有三个选项可以删除列表中的重复项:

1. 使用AA自定义相等比较,然后使用Distinct(new DistinctItemComparer())作为@Christian艾泰提及.

2. 使用GroupBy,但请注意GroupBy您应该按所有列分组,因为如果您只是按其分组,Id则不会始终删除重复的项目.例如,请考虑以下示例:

   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());
   

   此分组的结果将是:

   {Id = 1, Name = "Item1", Code = "IT00001", Price = 100}
   {Id = 2, Name = "Item2", Code = "IT00002", Price = 200}
   {Id = 3, Name = "Item3", Code = "IT00003", Price = 150}
   

   哪个不正确,因为它认为{Id = 3, Name = "Item3", Code = "IT00004", Price = 250}是重复的.所以正确的查询将是:

   var distinctItems = a.GroupBy(c => new { c.Id , c.Name , c.Code , c.Price})
                        .Select(c => c.First()).ToList();
   

   3.Override Equal和GetHashCode项目类:

   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();
       }
   }
   

   然后你可以像这样使用它:

   var distinctItems = a.Distinct();
   

Answer 7

通用扩展方法：

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);

Answer 8

试试这个扩展方法。希望这会有所帮助。

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);