Enumerable.Except<TSource> Method (IEnumerable<TSource>, IEnumerable<TSource>)

Type Parameters

• TSource
  The type of the elements of the input sequences.

Parameters

• first
  Type: System.Collections.Generic.IEnumerable<TSource>
  An IEnumerable<T> whose elements that are not also in second will be returned.

• second
  Type: System.Collections.Generic.IEnumerable<TSource>
  An IEnumerable<T> whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.

Return Value

Type: System.Collections.Generic.IEnumerable<TSource>
A sequence that contains the set difference of the elements of two sequences.

      ' Create two arrays of doubles.
      Dim numbers1() As Double = {2.0, 2.1, 2.2, 2.3, 2.4, 2.5}
      Dim numbers2() As Double = {2.2}

      ' Select the elements from the first array that are not
      ' in the second array.
      Dim onlyInFirstSet As IEnumerable(Of Double) = numbers1.Except(numbers2)

      Dim output As New System.Text.StringBuilder
      For Each number As Double In onlyInFirstSet
         output.AppendLine(number)
      Next

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

      ' This code produces the following output:
      '
      ' 2
      ' 2.1
      ' 2.3
      ' 2.4
      ' 2.5

      double[] numbers1 = { 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 };
      double[] numbers2 = { 2.2 };

      IEnumerable<double> onlyInFirstSet = numbers1.Except(numbers2);

      foreach (double number in onlyInFirstSet)
         outputBlock.Text += number + "\n";

      /*
       This code produces the following output:

       2
       2.1
       2.3
       2.4
       2.5
      */

Public Class Product
    Implements IEquatable(Of Product)

    Public Property Name As String
    Public Property Code As Integer

    Public Function Equals1(
        ByVal other As Product
        ) As Boolean Implements IEquatable(Of Product).Equals

        ' Check whether the compared object is null.
        If other Is Nothing Then Return False

        ' Check whether the compared object references the same data.
        If Me Is Other Then Return True

        ' Check whether the products' properties are equal.
        Return Code.Equals(other.Code) AndAlso Name.Equals(other.Name)
    End Function

    Public Overrides Function GetHashCode() As Integer

        ' Get hash code for the Name field if it is not null.
        Dim hashProductName = If(Name Is Nothing, 0, Name.GetHashCode())

        ' Get hash code for the Code field.
        Dim hashProductCode = Code.GetHashCode()

        ' Calculate the hash code for the product.
        Return hashProductName Xor hashProductCode
    End Function
End Class

public class Product : IEquatable<Product>
{
    public string Name { get; set; }
    public int Code { get; set; }

    public bool Equals(Product other)
    {

        //Check whether the compared object is null.
        if (Object.ReferenceEquals(other, null)) return false;

        //Check whether the compared object references the same data.
        if (Object.ReferenceEquals(this, other)) return true;

        //Check whether the products' properties are equal.
        return Code.Equals(other.Code) && Name.Equals(other.Name);
    }

    // If Equals() returns true for a pair of objects 
    // then GetHashCode() must return the same value for these objects.

    public override int GetHashCode()
    {

        //Get hash code for the Name field if it is not null.
        int hashProductName = Name == null ? 0 : Name.GetHashCode();

        //Get hash code for the Code field.
        int hashProductCode = Code.GetHashCode();

        //Calculate the hash code for the product.
        return hashProductName ^ hashProductCode;
    }
}

        Dim fruits1() As Product = 
            {New Product With {.Name = "apple", .Code = 9}, 
             New Product With {.Name = "orange", .Code = 4}, 
             New Product With {.Name = "lemon", .Code = 12}}

        Dim fruits2() As Product = 
            {New Product With {.Name = "apple", .Code = 9}}

        ' Get all the elements from the first array
        ' except for the elements from the second array.

        Dim except = fruits1.Except(fruits2)

        For Each product In except
            outputBlock.Text &= product.Name & " " & product.Code.ToString() & vbCrLf
        Next
        ' This code produces the following output:
        '
        ' orange 4
        ' lemon 12

        Product[] fruits1 = { new Product { Name = "apple", Code = 9 }, 
                               new Product { Name = "orange", Code = 4 },
                                new Product { Name = "lemon", Code = 12 } };

        Product[] fruits2 = { new Product { Name = "apple", Code = 9 } };

        //Get all the elements from the first array
        //except for the elements from the second array.

        IEnumerable<Product> except =
            fruits1.Except(fruits2);

        foreach (var product in except)
            outputBlock.Text += product.Name + " " + product.Code + "\n";

        /*
          This code produces the following output:

          orange 4
          lemon 12
        */