Group Number in a LINQ Group by Query

Question

I've been using 101 LINQ Samples to get my feet wet using LINQ. It's been a good first resource, but I can't see an example there of what I currently need.

I just need to associate a sequential group number with each group. I have a working solution:

var groups =
   from c in list
   group c by c.Name into details
   select new { Name = details.Key, DetailRecords = details };


int groupNumber = 0;
foreach (var group in groups)
{
   // 
   // process each group and it's records ...
   // 

   groupNumber++;
}

But, I'm sure it's possible to use LINQ to also generate the groupNumber. How?

Answer 1

this should do the trick:

int groupNumber = 0;
var groups =
   from c in list
   group c by c.Name into details
   select new { Name = details.Key, DetailRecords = details, grpNum = groupNumber++};

Answer 2

This depends on your exact needs, but you can use:

var groupArray = groups.ToArray();

Similarly, you can use ToList. These data structures are sequential, and each group has an index.

---

If you do need the index on the object you create, another option is to use Select:

list.GroupBy(c => c.Name)
    .Select((details, ind) =>
    new
    {
        Name = details.Key,
        DetailRecords = details,
        Index = ind
    });

Answer 3

if it's just a sequential group number, just use the Count() method on your IEnumerable.

var groups =
   from c in list
   group c by c.Name into details
   select new {Name = details.Key, DetailRecords = details};

for(int i = 0; i < groups.Count(); i++)
{
  //Process Records
}

Then, if you need the specific group number, you can just grab i.