Question

I have a collection of objects that each defined by a particular “group”. How can I write a LINQ query to produce a count of each object grouped by “group”.

As an example, lets say I have the following classes;

public class Release 
{
     int ReleaseNumber; 

     public ReleaseDetails[] details;

}

public class ReleaseDetails
{
    string Group;

    // other details omitted
}

For a given release, I’d like to be able to produce output like;

Release number 1 contains the following details;
 - 17 records in Group A
 - 12 records in Group B
 - 6 records in Group C

Any help is much appreciated.

Answer 1

You can do something like

var q = from d in r.Details
            group d by d.Group into counts
            select new { Count = counts.Count(), Group = counts.Key };

Full example:

        Release r = new Release
        {
            ReleaseNumber = 1
            ,
            Details = new ReleaseDetails[]
            {
                new ReleaseDetails { Group = "a"},
                new ReleaseDetails { Group = "a"},
                new ReleaseDetails { Group = "b"},
                new ReleaseDetails { Group = "c"},
                new ReleaseDetails { Group = "d"},
                new ReleaseDetails { Group = "d"},
                new ReleaseDetails { Group = "e"},

            }
        };

        var q = from d in r.Details
                group d by d.Group into counts
                select new { Count = counts.Count(), Group = counts.Key };

        foreach (var count in q)
        {
            Console.WriteLine("Group {0}: {1}", count.Group, count.Count);
        }