Question

I have a list of polylines(which i got by querying an access 2007 table) that holds the below values;

+----------+----------+----------+-------+
| 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 |
+----------+----------+----------+-------+

As the ObjectId column shows, there are only three objects. I would like to convert items from above list to a class in below format..

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

so that i can hold a List of Polyline objects and loop over each unique polyline as below..

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

}

What is the best/fast way of doing this in C#? It smells Linq..i am a total newbie to linq although very eager to learn and use it..

Answer 1

Assuming your List of polyline is a DataTable that holds all values:

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();