CODEWITHSUNDEEP
c#extension-methodsienumerable
user2023861
user2023861

Reputation: 8208

What's the Best Way to Add One Item to an IEnumerable<T>?

Here's how I would add one item to an IEnumerable object:

//Some IEnumerable<T> object
IEnumerable<string> arr = new string[] { "ABC", "DEF", "GHI" };

//Add one item
arr = arr.Concat(new string[] { "JKL" });

This is awkward. I don't see a method called something like ConcatSingle() however.

Is there a cleaner way to add a single item to an IEnumerable object?

Upvotes: 33

Views: 85550

Answers (6)

Gregory L
Gregory L

Reputation: 476

Append() - is exactly what you need, it has been added to the .NET Standard (in 2017), so you no longer need to write your own extension methods. You can simply do this:

arr = arr.Append("JKL");

Since .NET is open source, here you can look on the implementation (it is more sophisticated than custom methods suggested above): https://github.com/dotnet/runtime/blob/master/src/libraries/System.Linq/src/System/Linq/AppendPrepend.cs

Upvotes: 3

Soner G&#246;n&#252;l
Soner G&#246;n&#252;l

Reputation: 98840

Since IEnumerable is read-only, you need to convert to list.

var new_one = arr.ToList().Add("JKL");

Or you can get a extension method like;

public static IEnumerable<T> Append<T>(this IEnumerable<T> source, params T[] item)
{
    return source.Concat(item);
}

Upvotes: 7

cuongle
cuongle

Reputation: 75316

IEnumerable is immutable collection, it means you cannot add, or remove item. Instead, you have to create a new collection for this, simply to convert to list to add:

var newCollection = arr.ToList();
newCollection.Add("JKL"); //is your new collection with the item added

Upvotes: 9

Caelan
Caelan

Reputation: 1040

You're assigning an array to an IEnumerable. Why don't you use the Array type instead of IEnumerable?

Otherwise you can use IList (or List) if you want to change the collection.

I use IEnumerable only for methods params when I need to read and IList (or List) when I need to change items in it.

Upvotes: 2

LukeH
LukeH

Reputation: 269558

Nope, that's about as concise as you'll get using built-in language/framework features.

You could always create an extension method if you prefer:

arr = arr.Append("JKL");
// or
arr = arr.Append("123", "456");
// or
arr = arr.Append("MNO", "PQR", "STU", "VWY", "etc", "...");

// ...

public static class EnumerableExtensions
{
    public static IEnumerable<T> Append<T>(
        this IEnumerable<T> source, params T[] tail)
    {
        return source.Concat(tail);
    }
}

Upvotes: 23

Daniel Hilgarth
Daniel Hilgarth

Reputation: 174417

Write an extension method ConcatSingle :)

public static IEnumerable<T> ConcatSingle<T>(this IEnumerable<T> source, T item)
{
    return source.Concat(new [] { item } );
}

But you need to be more careful with your terminology.
You can't add an item to an IEnumerable<T>. Concat creates a new instance.

Example:

var items = Enumerable.Range<int>(1, 10)
Console.WriteLine(items.Count()); // 10
var original= items;
items = items.ConcatSingle(11);
Console.WriteLine(original.Count());   // 10
Console.WriteLine(items.Count()); // 11

As you can see, the original enumeration - which we saved in original didn't change.

Upvotes: 8

Related Questions