How to create a sequence of integers in C#?

Question

F# has sequences that allows to create sequences:

seq { 0 .. 10 }

Create sequence of numbers from 0 to 10.

Is there something similar in C#?

Solution 1

You can use Enumerable.Range(0, 10);. Example:

var seq = Enumerable.Range(0, 10);

MSDN page here.

Solution 2

Enumerable.Range(0, 11);

Generates a sequence of integral numbers within a specified range.

http://msdn.microsoft.com/en-us/library/system.linq.enumerable.range.aspx

Solution 3

You could create a simple function. This would work for a more complicated sequence. Otherwise the Enumerable.Range should do.

IEnumerable<int> Sequence(int n1, int n2)
{
    while (n1 <= n2)
    {
        yield return  n1++;
    }
}

Solution 4

Linq projection with the rarely used indexer overload (i):

(new int[11]).Select((o,i) => i)

I prefer this method for its flexibilty.

For example, if I want evens:

(new int[11]).Select((item,i) => i*2)

Or if I want 5 minute increments of an hour:

(new int[12]).Select((item,i) => i*5)

Or strings:

(new int[12]).Select((item,i) => "Minute:" + i*5)

Solution 5

In C# 8.0 you can use Indices and ranges

For example:

var seq = 0..2;
var array = new string[]
{
    "First",
    "Second",
    "Third",
};

foreach(var s in array[seq])
{
    System.Console.WriteLine(s);
}
// Output: First, Second

Or if you want create IEnumerable<int> then you can use extension:

public static IEnumerable<int> ToEnumerable(this Range range)
{
   for (var i = range.Start.Value; i < range.End.Value; i++)
   {
       yield return i;
   }
}
...
var seq = 0..2;

foreach (var s in seq.ToEnumerable())
{
   System.Console.WriteLine(s);
}
// Output: 0, 1

P.S. But be careful with 'indexes from end'. For example, ToEnumerable extension method is not working with var seq = ^2..^0.

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Comments

[Anthony Pegram]

Note: This creates a sequence starting at 0 with 10 items (ending at 9). If you want 0 through 10, the second parameter would be 11. And if you need an actual array and not IEnumerable<int>, include a call .ToArray().

[Zimano]

I really like this but it also feels a bit hacky at the same time!

[Zimano]

lol :-) It's just a great creative use of the indexer overload!

[ruffin]

By "more complicated" do you mean just "where you have begin and end handy instead of the number of elements"? Otherwise I'm missing your meaning. 🤔

[Aman]

I believe I was considering OddSequence EvenSequence or other custom ranges. if (++n1 % 2 == 0) yield return n1, for example. It's been a few days ;)

[ruffin]

Ha, yeah, one or two days I suppose. Or a few thousand. ;^)

[Matt Baran]

I feel like doing Enumerable.Range(0, 12).Select( i => "Minute:" + i*5 ) is more readable.