联合列表使用IEqualityComparer

时间:2016-04-14 07:01:45

标签: c# linq iequalitycomparer

我有两个班级名单Nomen:

var N1 = new List<Nomen>(); 
var N2 = new List<Nomen>(); 


public class Nomen
{
    public string Id;

    public string NomenCode;

    ...

    public string ProducerName;

    public decimal? minPrice;
}

我需要加入他们。我曾经这样做过:

result = N2.Union(N1, new NomenComparer()).ToList();

class NomenComparer : IEqualityComparer<Nomen>
{
    public bool Equals(Nomen x, Nomen y)
    {
        return x.Equals(y);
    }

    public int GetHashCode(Nomen nomen)
    {
        return nomen.GetHashCode();
    }
}

    public override int GetHashCode()
    {
        return (Id + NomenCode + ProducerName).GetHashCode();
    }

    public bool Equals(Nomen n)
    {
        if (!String.IsNullOrEmpty(Id) && Id == n.Id) return true;

        return (NomenCode == n.NomenCode && ProducerName == n.ProducerName);
    }

正如您所看到的,如果Ids或NomenCode和ProducerName相同,对我而言,它是相同的Nomen。 现在我的任务已经改变了,如果它们相等,我需要采取较少minPrice的任务。请帮我解决这个问题。 试图用linq做同样的事,但失败了

        var groups = (from n1 in N1
                      join n2 in N2
                      on new { n1.Id, n1.NomenCode, n1.ProducerName } equals new { n2.Id, n2.NomenCode, n2.ProducerName }
                      group new { n1, n2 } by new { n1.Id, n1.NomenCode, n1.ProducerName } into q
                      select new Nomen()
                      {
                          NomenCode = q.Key.NomenCode,
                          ProducerName = q.Key.ProducerName,
                          minPrice = q.Min(item => item.minPrice)
                      }).ToList();

主要是因为我需要加入Ids或{NomenCode,ProducerName}列表,我不知道该怎么做。

2 个答案:

答案 0 :(得分:4)

Concat,GroupBy然后再次选择?例如(比以前更少未经测试):

var nomens = N1.Concat(N2)
    .GroupBy(n=>n, new NomenComparer())
    .Select(group=>group.Aggregate( (min,n) => min == null || (n.minPrice ?? Decimal.MaxValue) < min.minPrice ? n : min));

答案 1 :(得分:1)

Linq加入OR条件已在此SO帖子中得到解答: Linq - left join on multiple (OR) conditions

简而言之,正如Jon Skeet在那篇文章中解释的那样,你应该做一些像

这样的事情
from a in tablea
from b in tableb
where a.col1 == b.col1 || a.col2 == b.col2
select ...