IOrderedEnumerable

With a C# query expression (beginning with from) we can sort a collection of elements. When we specify an orderby clause, an IOrderedEnumerable is returned.

An IOrderedEnumerable does the same thing an IEnumerable does, and we can use an IOrderedEnumerable variable where an IEnumerable is needed.

Example program

Consider now this program. We have a string array of 3 values. We use a query expression (starting with "from") to sort the values.

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        var animals = new string[] { "bird", "cat", "ant" };
        var result = from animal in animals
                     orderby animal ascending
                     select animal;
        // Our result is an IOrderedEnumerable.
        // ... We can use it as an IOrderedEnumerable.
        Test(result);
        // We can use the IOrderedEnumerable as an IEnumerable.
        Test2(result);
        // We can use extension methods for IEnumerable on IOrderedEnumerable.
        Console.WriteLine("Count: " + result.Count());
    }

    static void Test(IOrderedEnumerable<string> result)
    {
        // We can loop over an IOrderedEnumerable.
        foreach (string value in result)
        {
            Console.WriteLine("IOrderedEnumerable: " + value);
        }
    }

    static void Test2(IEnumerable<string> result)
    {
        foreach (string value in result)
        {
            Console.WriteLine("IEnumerable: " + value);
        }
    }
}
IOrderedEnumerable: ant
IOrderedEnumerable: bird
IOrderedEnumerable: cat
IEnumerable: ant
IEnumerable: bird
IEnumerable: cat
Count: 3

Notes

The program shows that "foreach" can be used on IOrderedEnumerable and IEnumerable. This is a common use for these interfaces—looping over them.

For most programs, we can focus on IEnumerable instead of IOrderedEnumerable. The distinction is not important. But it does indicate that the values have been sorted (by an orderby clause).