string.Join on a List or other type

Question

I want to turn an array or list of ints into a comma delimited string, like this:

string myFunction(List a) {
    return string.Join(\",\", a);
}
         


        

Answer 1

The best way is to upgrade to .NET 4.0 where there is an overload that does what you want:

• String.Join<T>(String, IEnumerable<T>)

If you can't upgrade, you can achieve the same effect using Select and ToArray.

    return string.Join(",", a.Select(x => x.ToString()).ToArray());

Answer 2

Using .NET 4.0

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string s = myFunction(PopulateTestList());
        this.TextBox1.Text = s;
    }

    protected List<int> PopulateTestList()
    {
        List<int> thisList = new List<int>();
        thisList.Add(22);
        thisList.Add(33);
        thisList.Add(44);

        return thisList;
    }

    protected string myFunction(List<int> a)
    {
        return string.Join(",", a);
    }
}

Answer 3

A scalable and safe implementation of a generic enumerable string join for .NET 3.5. The usage of iterators is so that the join string value is not stuck on the end of the string. It works correctly with 0, 1 and more elements:

public static class StringExtensions
{
    public static string Join<T>(this string joinWith, IEnumerable<T> list)
    {
        if (list == null)
            throw new ArgumentNullException("list");
        if (joinWith == null)
            throw new ArgumentNullException("joinWith");

        var stringBuilder = new StringBuilder();
        var enumerator = list.GetEnumerator();

        if (!enumerator.MoveNext())
            return string.Empty;

        while (true)
        {
            stringBuilder.Append(enumerator.Current);
            if (!enumerator.MoveNext())
                break;

            stringBuilder.Append(joinWith);
        }

        return stringBuilder.ToString();
    }
}

Usage:

var arrayOfInts = new[] { 1, 2, 3, 4 };
Console.WriteLine(",".Join(arrayOfInts));

var listOfInts = new List<int> { 1, 2, 3, 4 };
Console.WriteLine(",".Join(listOfInts));

Enjoy!

Answer 4

.NET 2.0:

static string IntListToDelimitedString(List<int> intList, char Delimiter)
{
    StringBuilder builder = new StringBuilder();

    for (int i = 0; i < intList.Count; i++)
    {
        builder.Append(intList[i].ToString());

        if (i != intList.Count - 1)
            builder.Append(Delimiter);
    }

    return builder.ToString();
}

Answer 5

This answer is for you if you don't want to venture into the depths of .NET 4.0 just yet.

String.Join() concatenates all the elements of a string array, using the specified separator between each element.

The syntax is

public static string Join(
    string separator,
    params string[] value
)

Rather than passing your List of ints to the Join method, I suggest building up an array of strings first.

Here is what I propose:

static string myFunction(List<int> a) {
    int[] intArray = a.ToArray();
    string[] stringArray = new string[intArray.Length];

    for (int i = 0; i < intArray.Length; i++)
    {
        stringArray[i] = intArray[i].ToString();
    }

    return string.Join(",", stringArray);
}

Answer 6

In .NET the list class has a .ToArray() method. Something like this could work:

string myFunction(List<int> a)
{
    return string.Join(",", a.ToArray());
}

Ref: List<T> Methods (MSDN)