Question

我有一个折线列表（通过查询访问2007表获得），其中包含以下值;

+----------+----------+----------+-------+
| ObjectID | VertexId | distance | angle |
+----------+----------+----------+-------+
|        1 |        0 |       10 |    45 |
|        1 |        1 |       10 |    44 |
|        1 |        2 |       20 |    60 |
|        2 |        0 |        5 |    35 |
|        2 |        1 |        6 |    35 |
|        2 |        2 |        4 |    56 |
|        2 |        3 |       12 |    45 |
|        3 |        0 |       20 |    30 |
|        3 |        1 |       10 |    12 |
+----------+----------+----------+-------+

如ObjectId列所示，只有三个对象。我想将上面列表中的项目转换为以下格式的类..

Class Polyline
{
    int ObjectID;
    list<int> vertices;
    list<double> distances;
    list<double> angles;
}

这样我就可以保存一条Polyline对象并在每条唯一折线上循环，如下所示。

foreach(Polyline polyObj in Polylines)
{
    //do something with the polyline object;

}

在C＃中执行此操作的最佳/最快方法是什么？它闻起来Linq ..我是linq的新手，虽然非常渴望学习和使用它..

Answer 1

假设您的折线列表是DataTable，其中包含所有值：

List<Polyline> polylines =
    tblPolyline.AsEnumerable()
   .GroupBy(p => p.Field<int>("ObjectID"))
   .Select(grp => new Polyline()
   {
       ObjectID = grp.Key,
       Vertices = new List<int>(grp.Select(p => p.Field<int>("VertexId"))),
       Distances = new List<double>(grp.Select(p => p.Field<double>("distance"))),
       Angles = new List<double>(grp.Select(p => p.Field<double>("angle"))),
   }).ToList();

Answer 2

考虑将顶点移动到单独的类：

public class PolyLine
{
    public PolyLine(int id, IEnumerable<Vertex> vertices)
    {
        Id = id;
        Vertices = new List<Vertex>(vertices);
    }

    public int Id { get; private set; }
    public List<Vertex> Vertices { get; private set; }
}

public class Vertex
{
    public Vertex(int id, int distance, int angle)
    {
        Id = id;
        Distance = distance;
        Angle = angle;
    }

    public int Id { get; private set; }
    public int Distance { get; private set; }
    public int Angle { get; private set; }
}

这是LINQ创建折线：

var polylines = from r in records
                group r by r.ObjectID into g
                select new PolyLine(g.Key, g.Select(r => new Vertex(r.VertexId, r.Distance, r.Angle)));

更新：LINQ to DataSet版本

var polylines = from r in table.AsEnumerable()
                group r by r.Field<int>("ObjectID") into g
                select new PolyLine(g.Key, 
                             g.Select(r => new Vertex(r.Field<int>("VertexId"),
                                                      r.Field<int>("distance"), 
                                                      r.Field<int>("angle"))));

将列表转换为不同的类结构

2 个答案: