Lookup<TKey, TElement> Class

Type Parameters

• TKey
  The type of the keys in the Lookup<TKey, TElement>.

• TElement
  The type of the elements of each IEnumerable<T> value in the Lookup<TKey, TElement>.

Structure Package
   Public Company As String
   Public Weight As Double
   Public TrackingNumber As Long
End Structure

Sub LookupExample()
   ' Create a list of Packages to put into a Lookup data structure.
   Dim packages As New System.Collections.Generic.List(Of Package)(New Package() _
       {New Package With {.Company = "Coho Vineyard", .Weight = 25.2, .TrackingNumber = 89453312L}, _
         New Package With {.Company = "Lucerne Publishing", .Weight = 18.7, .TrackingNumber = 89112755L}, _
         New Package With {.Company = "Wingtip Toys", .Weight = 6.0, .TrackingNumber = 299456122L}, _
         New Package With {.Company = "Contoso Pharmaceuticals", .Weight = 9.3, .TrackingNumber = 670053128L}, _
         New Package With {.Company = "Wide World Importers", .Weight = 33.8, .TrackingNumber = 4665518773L}})

   ' Create a Lookup to organize the packages. Use the first character of Company as the key value.
   ' Select Company appended to TrackingNumber for each element value in the Lookup.
   Dim lookup As ILookup(Of Char, String) = _
       packages.ToLookup(Function(p) Convert.ToChar(p.Company.Substring(0, 1)), _
                         Function(p) p.Company & " " & p.TrackingNumber)

   Dim output As New System.Text.StringBuilder
   ' Iterate through each Example in the Lookup and output the contents.
   For Each packageGroup As IGrouping(Of Char, String) In lookup
      ' Print the key value of the Example.
      output.AppendLine(packageGroup.Key)
      ' Iterate through each value in the Example and print its value.
      For Each str As String In packageGroup
         output.AppendLine(String.Format("    {0}", str))
      Next
   Next

   ' Display the output.
   outputBlock.Text &= output.ToString() & vbCrLf

   ' This code produces the following output:
   '
   ' C
   '     Coho Vineyard 89453312
   '     Contoso Pharmaceuticals 670053128
   ' L
   '     Lucerne Publishing 89112755
   ' W
   '     Wingtip Toys 299456122
   '     Wide World Importers 4665518773

   ' Get the number of key-collection pairs in the Lookup.
   Dim count As Integer = lookup.Count

   ' Select a collection of Packages by indexing directly into the Lookup.
   Dim cgroup As System.Collections.Generic.IEnumerable(Of String) = lookup("C"c)

   output = New System.Text.StringBuilder
   ' Output the results.
   output.AppendLine(vbCrLf & "Packages that have a key of 'C':")
   For Each str As String In cgroup
      output.AppendLine(str)
   Next

   ' Display the output.
   outputBlock.Text &= output.ToString() & vbCrLf

   ' This code produces the following output:
   '
   ' Packages that have a key of 'C'
   ' Coho Vineyard 89453312
   ' Contoso Pharmaceuticals 670053128

   ' Determine if there is a key with the value 'G' in the Lookup.
   Dim hasG As Boolean = lookup.Contains("G"c)
End Sub

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

public static void LookupExample(System.Windows.Controls.TextBlock outputBlock)
{
   // Create a list of Packages to put into a Lookup data structure.
   List<Package> packages = new List<Package> { new Package { Company = "Coho Vineyard", 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 = "Contoso Pharmaceuticals", Weight = 9.3, TrackingNumber = 670053128L },
                                                new Package { Company = "Wide World Importers", Weight = 33.8, TrackingNumber = 4665518773L } };

   // Create a Lookup to organize the packages. Use the first character of Company as the key value.
   // Select Company appended to TrackingNumber for each element value in the Lookup.
   Lookup<char, string> lookup = (Lookup<char, string>)packages.ToLookup(p => Convert.ToChar(p.Company.Substring(0, 1)),
                                                   p => p.Company + " " + p.TrackingNumber);

   // Iterate through each Example in the Lookup and output the contents.
   foreach (IGrouping<char, string> packageGroup in lookup)
   {
      // Print the key value of the Example.
      outputBlock.Text += packageGroup.Key + "\n";
      // Iterate through each value in the Example and print its value.
      foreach (string str in packageGroup)
         outputBlock.Text += String.Format("    {0}", str) + "\n";
   }

   // This code produces the following output:
   //
   // C
   //     Coho Vineyard 89453312
   //     Contoso Pharmaceuticals 670053128
   // L
   //     Lucerne Publishing 89112755
   // W
   //     Wingtip Toys 299456122
   //     Wide World Importers 4665518773

   // Get the number of key-collection pairs in the Lookup.
   int count = lookup.Count;

   // Select a collection of Packages by indexing directly into the Lookup.
   IEnumerable<string> cgroup = lookup['C'];

   // Output the results.
   outputBlock.Text += "\nPackages that have a key of 'C':" + "\n";
   foreach (string str in cgroup)
      outputBlock.Text += str + "\n";

   // This code produces the following output:
   //
   // Packages that have a key of 'C'
   // Coho Vineyard 89453312
   // Contoso Pharmaceuticals 670053128

   // Determine if there is a key with the value 'G' in the Lookup.
   bool hasG = lookup.Contains('G');
}