Create an enumeration of one

Question

If I want an empty enumeration, I can call Enumerable.Empty<T>(). But what if I want to convert a scalar type to an enumeration?

Normally I'd write new List<string> {myString} to pass myString to a function that accepts IEnumerable<string>. Is there a more LINQ-y way?

Answer 1

You can use Repeat:

var justOne = Enumerable.Repeat(value, 1);

Or just an array of course:

var singleElementArray = new[] { value };

The array version is mutable of course, whereas Enumerable.Repeat isn't.

Answer 2

Perhaps the shortest form is

var sequence = new[] { value };

Answer 3

There is, but it's less efficient than using a List or Array:

// an enumeration containing only the number 13.
var oneIntEnumeration = Enumerable.Repeat(13, 1);

Answer 4

You can also write your own extension method:

public static class Extensions
{
    public static IEnumerable<T> AsEnumerable<T>(this T item)
    {
         yield return item;
    }
}

Now I haven't done that, and now that I know about Enumerable.Repeat, I probably never will (learn something new every day). But I have done this:

public static IEnumerable<T> MakeEnumerable<T>(params T[] items)
{
     return items;
}

And this, of course, works if you call it with a single argument. But maybe there's something like this in the framework already, that I haven't discovered yet.