How to use Distinct in a column using Linq

Question

Here is my code:

var query = from row1 in table.AsEnumerable()
                         let time = row1.Field<DateTime>("time")
                         let uri = row1.Field<string>("cs-uri-stem")
                         let ip = row1.Field<string>("c-ip")
                         let questionid = row1.Field<int>("questionid")
                         where questionid == int.Parse(table.Rows[x]["questionid"].ToString())
                         select new
                         {
                             time,
                             uri,
                             ip,
                             questionid
                         };

The ip column must be unique. I cannot duplicate elements in ip field. is it possible to do this in linq

Answer 1

You can achieve what you want by grouping by IP address, but then you need to know how you want to handle other fields when you have duplicates.

var query = from row1 in table.AsEnumerable()
                     let time = row1.Field<DateTime>("time")
                     let uri = row1.Field<string>("cs-uri-stem")
                     let ip = row1.Field<string>("c-ip")
                     let questionid = row1.Field<int>("questionid")
                     where questionid == int.Parse(table.Rows[x]["questionid"].ToString())
                     group by ip into g
                     select new
                     {
                         time = g.time.First(),
                         uri = g.uri.First(),
                         ip = g.Key,
                         questionid = g.questionid.First()
                     };

Answer 2

You can only execute Distinctin all fields of your choice, and not just on one field (what values ​​would you take for other fields?).

You can achieve this using the extension method Distinct:

        var query = (from row1 in table.AsEnumerable()
                     let time = row1.Field<DateTime>("time")
                     let uri = row1.Field<string>("cs-uri-stem")
                     let ip = row1.Field<string>("c-ip")
                     let questionid = row1.Field<int>("questionid")
                     where questionid == int.Parse(table.Rows[x]["questionid"].ToString())
                     select new
                     {
                         time,
                         uri,
                         ip,
                         questionid
                     }).Distinct();

Answer 3

Distinct() (.. , IP, ). tvanfosson, ?