LINQ: A better way to grouping a list of objects by multiple properties in to a list of lists?

Question

I have a list of objects as such:

var cmps = new List<Campaign>()
{
    new Campaign(){ PersonId = 1, Id = 1, Name = "Name"},
    new Campaign(){ PersonId = 2, Id = 1, Name = "Name"},
    new Campaign(){ PersonId = 3, Id = 1, Name = "Name1"},                
    new Campaign(){ PersonId = 4, Id = 2, Name = "Name1"},                
    new Campaign(){ PersonId = 5, Id = 2, Name = "Name1"},
    new Campaign(){ PersonId = 6, Id = 3, Name = "Name"},
};

I want to group them into a list of lists by the multiple properties, in this example by Id and Name.

This would split the original list into the following (where the number represents PersonId):

{[1, 2], [3], [4, 5], [6]}

I have solved this by writing the following code:

List<List<Campaign>> groups = cmps.GroupBy(c => new { c.Id, c.Name })
                                  .Select(c => c.Key)
                                  .ToList()
                                  .Select(v => cmps.Where(c => c.Id == v.Id && c.Name == v.Name).ToList())
                                  .ToList();

This solution seems to be working fine, but out of curiosity, is there a nicer/better way to do this?

Answer 1

Just do:

List<List<Campaign>> groups = cmps.GroupBy(c => new { c.Id, c.Name })
    .Select(group => group.ToList())
    .ToList();

GroupBy on IEnumerable returns IEnumerable<IGrouping<TKey, T>>. IGrouping<TKey, T> implements IEnumerable<T>, so you can just use the group directly as a sequence.