Using linq to group, select, and order a datatable

Question

I want to use Linq to select and group DataTable rows... and I want to order those in a descending manner by the "Max" created date in each group... are there any improvements that could be made to this code, in particular can I make the OrderByDescending part of the Linq, for example using:

                    orderby {... something here...} descending

--- current code ---

        DataTable dt = ReadDataTable();
        var rows = (from row in dt.AsEnumerable()
                    where row.Field<bool>("Active") == true
                    group row by new
                    {
                        CollectionId = row.Field<int>("CollectionId"),
                        CollectionName = row.Field<string>("CollectionName"),
                    } into grp
                    select new
                    {
                        CollectionId = grp.Key.CollectionId,
                        CollectionName = grp.Key.CollectionName,
                        MaxCreated = grp.Max(r => r.Field<DateTime>("Created"))
                    }).OrderByDescending(r => r.MaxCreated);

Is this a duplicate of Linq order by aggregate in the select { }? — dbc
– dbc, Commented Mar 13, 2016 at 19:36

dbc · Accepted Answer · 2016-03-13 19:21:23Z

You can use the let clause to hold intermediate results in a complex LINQ query, for use in subsequent sorts and selects. In your case you can use it to store the final result for subsequent sorting.

I.e. you can rewrite your Linq without the OrderByDescending() lambda as follows:

DataTable dt = ReadDataTable();
var rows = from row in dt.AsEnumerable()
           where row.Field<bool>("Active")
           group row by new
           {
               CollectionId = row.Field<int>("CollectionId"),
               CollectionName = row.Field<string>("CollectionName"),
           } into grp
           let result = new
           {
               CollectionId = grp.Key.CollectionId,
               CollectionName = grp.Key.CollectionName,
               MaxCreated = grp.Max(r => r.Field<DateTime>("Created")),
           }
           orderby result.MaxCreated descending
           select result;

Collectives™ on Stack Overflow

Using linq to group, select, and order a datatable

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related