I have a below code that create a dictionary from List. How can I group the dictionary base of company. As you can see Company = "Adventure" is twice in the list. So total dictionary records will be 3

class Package
{
    public string Company { get; set; }
    public double Weight { get; set; }
    public long TrackingNumber { get; set; }
}

public static void ToDictionaryEx1()
{
    List<Package> packages =
        new List<Package>
            { new Package { Company = "Adventure", Weight = 25.2, TrackingNumber = 89453312L },
              new Package { Company = "Lucerne Publishing", Weight = 18.7, TrackingNumber = 89112755L },
              new Package { Company = "Wingtip Toys", Weight = 6.0, TrackingNumber = 299456122L },
              new Package { Company = "Adventure", Weight = 33.8, TrackingNumber = 4665518773L } };

    // Create a Dictionary of Package objects,
    // using TrackingNumber as the key.
    Dictionary<long, Package> dictionary =
        packages.ToDictionary(p => p.Company);

   
}

I am trying group by but some how not working

  data.GroupBy(
                        x => x.Source,
                        (k, x) => new
                        {
                            Source = k,
                            Promotions = x.
                                .ToList()
                        })
                    .ToDictionary(x => x.Source, x => x.Promotions);

CodePudding user response：

No need to make the Linq GroupBy so complicated, simply define the key, then use ToDictionary based on the key and the grouped values.

Dictionary<string, List<Package>> dictionary = packages
    .GroupBy(p => p.Company)
    .ToDictionary(g => g.Key, g => g.ToList());

The key of the dictionary is a string not a long because you want to group by the CompanyName (which is a string).

Online example

CodePudding user response：

The ILookup structure allows you to group items with the same key:

packages.ToLookup(p => p.Company, p => p)

I don't know whether it is suitable structure for your needs, but with this approach you don't need to call GroupBy explicitly.

With that the result would look like this:

Dumping object(System.Linq.Lookup`2[String,Package])
[
   {
[
       {
       Company         : Adventure
       TrackingNumber  : 89453312
       Weight          : 25.2
       },
       {
       Company         : Adventure
       TrackingNumber  : 4665518773
       Weight          : 33.8
       }
]   },
   {
[
       {
       Company         : Lucerne Publishing
       TrackingNumber  : 89112755
       Weight          : 18.7
       }
]   },
   {
[
       {
       Company         : Wingtip Toys
       TrackingNumber  : 299456122
       Weight          : 6
       }
]   }
]