Question

Language: C# 4.0

There is a List<string> with values Value1, Value2, Value3 and so on.
I would like to perform a join on the generic List so that the output should be

string values = "Value1, Value2 and Value3"; 

and if there is only one value

string values = "Value1"; 

I am currently replacing LastIndexOf , with and. But did not like that much.
Whats the most efficient method to join like this?

Answer 1

You can use the String.Join(string glue, string[] array); function for this.

string values = String.Join(", ", myList.ToArray());

Hope that helps. (Note: myList is the List you already have in your application somewhere.)

Update: Noticed your and requirement a little too late, my appologies, here is a little update:

string values = String.Join(", ", myList.Take(myList.Count - 1)) 
                   + " and " + myList.Last();

Alternatively (or maybe even better) you can use a StringBuilder for this, instead of string concatenation. (Remember: You will still have to check if you have only one value in the list.)

Update: Here is a simple extension method.

public static string SmartJoin(this List<string> items, string lastSeparator)
{
    string values = "";
    if(!items.Any())
    {
        return "";
    }
    if (items.Count > 1)
    {
        values = String.Format("{0} {1} {2}",
                    String.Join(", ", items.Take(items.Count - 1)),
                    lastSeparator,
                    items.Last());
    }
    else
    {
        values = items.First();
    }
    return values;
}

And one can call it like

string values = myList.SmartJoin("and");