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Populating a list of integers in .NET

Posted by: admin November 29, 2017 Leave a comment

Questions:

I need a list of integers from 1 to x where x is set by the user. I could build it with a for loop eg assuming x is an integer set previously:

List<int> iList = new List<int>();
for (int i = 1; i <= x; i++)
{
    iList.Add(i);
}

This seems dumb, surely there’s a more elegant way to do this, something like the PHP range method

Answers:

If you’re using .Net 3.5, Enumerable.Range is what you need.

Generates a sequence of integral
numbers within a specified range.

Questions:
Answers:

LINQ to the rescue:

// Adding value to existing list
var list = new List<int>();
list.AddRange(Enumerable.Range(1, x));

// Creating new list
var list = Enumerable.Range(1, x).ToList();

See Generation Operators on LINQ 101

Questions:
Answers:

I’m one of many who has blogged about a ruby-esque To extension method that you can write if you’re using C#3.0:


public static class IntegerExtensions
{
    public static IEnumerable<int> To(this int first, int last)
    {
        for (int i = first; i <= last; i++)
{ yield return i; } } }

Then you can create your list of integers like this

List<int> = first.To(last).ToList();

or

List<int> = 1.To(x).ToList();

Questions:
Answers:

Here is a short method that returns a List of integers.

    public static List<int> MakeSequence(int startingValue, int sequenceLength)
    {
        return Enumerable.Range(startingValue, sequenceLength).ToList<int>();
    }