Enumerable.Range

A sequence of numbers progresses in order: 10, 11, 12, 13. With Enumerable.Range, each number is one greater than the previous.

Similar to Range, we can invoke Enumerable.Repeat and Enumerable.Empty. Repeat duplicates a value many times. Empty(), meanwhile, returns no values.

Range example

Let us begin. We invoke Enumerable.Range (part of the System.Linq namespace). We use foreach to loop over all the numbers in the resulting sequence.

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

class Program
{
    static void Main()
    {
        // Generate a range of number starting at 5.
        // ... First parameter is the start number.
        //     Second parameter is the count of numbers (not the last index).
        IEnumerable<int> numbers = Enumerable.Range(5, 3);
        foreach (int n in numbers)
        {
            Console.WriteLine(n);
        }
    }
}
5
6
7

Count error

The second argument to Enumerable.Range must be 0 or greater. Here we get an error when we try to create a sequence of negative 1 length.

using System.Linq;

class Program
{
    static void Main()
    {
        // This will cause an exception.
        var numbersNegative = Enumerable.Range(10, -1);
    }
}
Unhandled Exception: System.ArgumentOutOfRangeException:
Specified argument was out of the range of valid values.
Parameter name: count
   at System.Linq.Enumerable.Range(Int32 start, Int32 count)
   at Program.Main()...

Repeat example

This returns a collection with repeated elements. Enumerable.Repeat is located in the System.Linq namespace. Please add the "using" directive at the top of the program.

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        // Create sequence of 10 ones.
        var integers = Enumerable.Repeat(1, 10);

        // Display.
        foreach (int value in integers)
        {
            Console.WriteLine("REPEAT: {0}", value);
        }
    }
}
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1
REPEAT: 1

Empty example

Enumerable.Empty generates an IEnumerable of zero elements. It can be used when you want to avoid a query expression and instead just want to use an empty sequence.

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        var empty = Enumerable.Empty<int>();
        Console.WriteLine(empty.Count());
        int[] array = empty.ToArray();
        Console.WriteLine(array.Length);
    }
}
0
0

Combine methods

A benefit of Enumerable.Range, Repeat (and even Empty) is that we can combine them with other extension methods. Here we want to sum numbers up to a certain value.

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        while (true)
        {
            // Get user input.
            Console.WriteLine("SUM UP TO:");
            string result = Console.ReadLine();

            // Parse number.
            if (int.TryParse(result, out int number))
            {
                // Call Sum() on Enumerable.Range.
                int sum = Enumerable.Range(0, number + 1).Sum();
                Console.WriteLine("RESULT: {0}", sum);
            }
        }
    }
}
SUM UP TO:
3
RESULT: 6
SUM UP TO:
4
RESULT: 10
SUM UP TO:
100
RESULT: 5050
SUM UP TO:

Windows Forms example

This code is a little different. We use a call to Enumerable.Range to create a control's contents in Windows Forms.

public partial class ReporterWindow : Form
{
    public ReporterWindow()
    {
        InitializeComponent();

        //
        // Add "using System.Linq;" at the top of your source code.
        // ... Use an array from Enumerable.Range.
        // ... Set it to the data source of the DropDown boxes.
        //
        xComboBox.DataSource = Enumerable.Range(0, 15).ToArray();
        yComboBox.DataSource = Enumerable.Range(0, 15).ToArray();
    }
}

Range, notes

The Range method, with ToArray, returns the entire array needed. This may be easier to read. Expressions encapsulate logic into a single statement.

Empty, implementation

Empty() uses a static generic type and then calls a property (Instance) on that type. An empty array is lazily initialized in the Instance property.

Convert, notes

We can convert the IEnumerable result from these methods to an array or List. Please use the ToArray or ToList extension methods and assign the result.

A warning

Using the Enumerable.Range method will have performance negatives over iterative approaches due to the overhead of LINQ. These negatives must be considered.

With Repeat and Empty, we can get IEnumerables in the same way as Range, but with different values. These methods can be used with queries to help improve program clarity.