Comma “izing” a list of items

Question

Given a list of strings, what is the best method for concatenating these strings into a comma separated list with no comma at the end. (VB.NET or C#) (Using either StringBuilder

Answer 1

Like this:

lstItems.ToConcatenatedString(s => s, ", ")

If you want to ignore empty strings as in your example:

lstItems
    .Where(s => s.Length > 0)
    .ToConcatenatedString(s => s, ", ")

The most popular custom aggregate function in my toolbox. I use it every day:

public static class EnumerableExtensions
{

    /// 

    /// Creates a string from the sequence by concatenating the result
    /// of the specified string selector function for each element.
    /// 
    public static string ToConcatenatedString(
        this IEnumerable source,
        Func stringSelector)
    {
        return EnumerableExtensions.ToConcatenatedString(source, stringSelector, String.Empty);
    }

    /// 

    /// Creates a string from the sequence by concatenating the result
    /// of the specified string selector function for each element.
    /// 
    /// The string which separates each concatenated item.
    public static string ToConcatenatedString(
        this IEnumerable source,
        Func stringSelector,
        string separator)
    {
        var b = new StringBuilder();
        bool needsSeparator = false; // don't use for first item

        foreach (var item in source)
        {
            if (needsSeparator)
                b.Append(separator);

            b.Append(stringSelector(item));
            needsSeparator = true;
        }

        return b.ToString();
    }
}