Introduction

Filtering, as the name suggests, refers to the operation of filtering the result set so that it contains only those elements that satisfy a specified given condition. The Where clause is used as the Filtering operator in LINQ. The Where clause is used to filter a sequence based on a given condition. The syntax of using the Where clause with LINQ is:

public static IEnumerable<T> where <T> (this IEnumerable<T> source, Function<T, bool> predicate);

The Where clause is used in a query expression to specify which elements from the data source will be returned in the query expression. For example, you can use the Where clause to filter numbers except those that are less than 5.

Lets take an simple example 

Step-1 : Add one ListBox and Button control on design window
.
<form id="form1" runat="server">
    <div>        
        <span class="style1"><strong>Example of Filtering type operator in LINQ</strong></span><br />
        <asp:ListBox ID="ListBox1" runat="server"></asp:ListBox>
        <br />
        <br />
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
            Text="Add item to the List" />        
        <br />
    </div>
    </form>
Step-2 : Handle business logic code on Button Click event.
Step-3 : Create Object type array with different type values.

  object[] data = { 10, "ten", 20, "twenty", 30, "thirty" };

Step-4 : Select filter type using OfType<string>(); extension IEnumerable.
Step-5 : Add filtered value into ListBox.

Output of given below code