使用LINQ对备用对进行分组

Question

我正在尝试对包含备用族对的DTO列表进行分组,以便按以下格式对它们进行分组,以最大限度地减少重复.

这是我目前的DTO结构,它有重复的行,你可以看到它们也可以根据反向关系组合在一起.

+----------+------------+-----------+
| PersonId | RelativeId | Relation  |
+----------+------------+-----------+
|        1 |          2 | "Son"     |
|        2 |          1 | "Father"  |
|        1 |          3 | "Mother"  |
|        3 |          1 | "Son"     |
|        2 |          3 | "Husband" |
|        3 |          2 | "Wife"    |
+----------+------------+-----------+

进入这样的事情:

+----------+------------+-----------+-----------------+
| PersonId | RelativeId | Relation  | ReverseRelation |
+----------+------------+-----------+-----------------+
|        1 |          2 | "Son"     | "Father"        |
|        1 |          3 | "Mother"  | "Son"           |
|        2 |          3 | "Husband" | "Wife"          |
+----------+------------+-----------+-----------------+

---

我正在尝试的代码:

Program.cs中

class Program
{
    static void Main(string[] args)
    {
        List<RelationDTO> relationDTOList = new List<RelationDTO>
        {
            new RelationDTO { PersonId = 1, RelativeId = 2, Relation = "Son" },
            new RelationDTO { PersonId = 2, RelativeId = 1, Relation = "Father" },

            new RelationDTO { PersonId = 1, RelativeId = 3, Relation = "Mother" },
            new RelationDTO { PersonId = 3, RelativeId = 1, Relation = "Son" },

            new RelationDTO { PersonId = 2, RelativeId = 3, Relation = "Husband" },
            new RelationDTO { PersonId = 3, RelativeId = 2, Relation = "Wife" },
        };

        var grp = relationDTOList.GroupBy(x => new { x.PersonId }).ToList();
    }
}

RelationDTO.cs

public class RelationDTO
{
    public int PersonId { get; set; }
    public int RelativeId { get; set; }
    public string Relation { get; set; }
}

Relations.cs

public class Relations
{
    public int PersonId { get; set; }
    public int RelativeId { get; set; }
    public string Relation { get; set; }
    public string ReverseRelation { get; set; }
}

Answer 1

您可以使用类似的连接操作

var result = relationDTOList
.Where(v => v.PersonId < v.RelativeId)
.Join(
    relationDTOList.Where(v => v.PersonId > v.RelativeId),
    v => new Key{PersonId = v.PersonId, RelativeId = v.RelativeId},
    v => new Key{PersonId = v.RelativeId, RelativeId = v.PersonId},
    (p, q) => new Relations
    {
        PersonId = p.PersonId,
        RelativeId = p.RelativeId,
        Relation = p.Relation,
        ReverseRelation = q.Relation
    }
);

该Key方法是:

public struct Key
{
    public int PersonId { get; set; }
    public int RelativeId { get; set; }
}

Answer 2

我不确定这是否是你需要的:

public static void Main()
{
    List<RelationDTO> relationDTOList = new List<RelationDTO>
    {
        new RelationDTO { PersonId = 1, RelativeId = 2, Relation = "Son" },
        new RelationDTO { PersonId = 2, RelativeId = 1, Relation = "Father" },

        new RelationDTO { PersonId = 1, RelativeId = 3, Relation = "Mother" },
        new RelationDTO { PersonId = 3, RelativeId = 1, Relation = "Son" },

        new RelationDTO { PersonId = 2, RelativeId = 3, Relation = "Husband" },
        new RelationDTO { PersonId = 3, RelativeId = 2, Relation = "Wife" },
    };

    var grp = relationDTOList.Join(relationDTOList, 
            dto => dto.PersonId + "-" + dto.RelativeId, 
            dto => dto.RelativeId + "-" + dto.PersonId, 
    (dto1, dto2) => new Relations 
            { 
                PersonId = dto1.PersonId, 
                RelationId = dto1.RelativeId, 
                Relation = dto1.Relation, 
                ReverseRelation = dto2.Relation 
                }).Distinct(new MyEqualityComparer());

    foreach (var g in grp)
        Console.WriteLine("{0},{1},{2},{3}", g.PersonId, g.RelationId, g.Relation, g.ReverseRelation);
}

public class MyEqualityComparer : IEqualityComparer<Relations>
{
    public bool Equals(Relations x, Relations y)
    {
        return x.PersonId + "-" + x.RelationId == y.PersonId + "-" + y.RelationId || 
        x.PersonId + "-" + x.RelationId == y.RelationId + "-" + y.PersonId;
    }

    public int GetHashCode(Relations obj)
    {
        return 0;
    }
}

Answer 3

我怀疑LINQ是最好的选择,因为查找循环可能会更有效率.但是,如果您真的需要LINQ,那么您可以执行以下操作

var relations = from person in relationDTOList
    // Match on the exact pair of IDs
    join relative in relationDTOList on
        new { person.PersonId, person.RelativeId } equals
        new { PersonId = relative.RelativeId, RelativeId = relative.PersonId }

    // Build the new structure
    let relation = new Relations {
        PersonId = person.PersonId,
        Relation = person.Relation,
        RelativeId = relative.PersonId,
        ReverseRelation = relative.Relation
    }

    // Order the pairs to find the duplicates
    let ids = new[] {person.PersonId, relative.PersonId}.OrderBy(x => x).ToArray()
    group relation by new { FirstPersonId = ids[0], SecondPersonId = ids[1] }
    into relationGroups

    // Select only the the first of two duplicates
    select relationGroups.First();

此代码所做的是将集合与自身连接在匹配对上PersonId,RelativeId然后过滤掉每对中的第二条记录,从而生成一个集合,其中列表中找到的第一个人将被视为关系中的父级.

编辑:我正在谈论的查找方法:

var result = new List<Relations>();
while (relationDTOList.Any())
{
    var person = relationDTOList.First();
    relationDTOList.RemoveAt(0);

    var relative = relationDTOList.Where(x =>
            x.PersonId == person.RelativeId && x.RelativeId == person.PersonId)
        .Select((x, i) => new {Person = x, Index = i}).FirstOrDefault();

    if (relative != null)
    {
        relationDTOList.RemoveAt(relative.Index);
        result.Add(new Relations {
            PersonId = person.PersonId,
            Relation = person.Relation,
            RelativeId = relative.Person.PersonId,
            ReverseRelation = relative.Person.Relation
        });
    }
}

作为一个注释,它会清空您的原始列表,因此list.ToList()如果您需要在代码中进一步需要,则必须复制().

运行此代码的速度比join我之前发布的方法快六倍.我还提出了以下分组方法,它比连接运行得快得多,但它仍然比查找和删除方法慢,尽管它们做的非常类似.

var relations = relationDTOList.GroupBy(person =>
        person.PersonId < person.RelativeId
            ? new {FirstPersonId = person.PersonId, SecondPersonId = person.RelativeId}
            : new {FirstPersonId = person.RelativeId, SecondPersonId = person.PersonId})

    .Select(group => new Relations {
        PersonId = group.First().PersonId,
        Relation = group.First().Relation,
        RelativeId = group.First().RelativeId,
        ReverseRelation = group.Last().Relation
    });