Converting a generic list to a CSV string

List<int> myValues;

string csv = String.Join(",", myValues.Select(x => x.ToString()).ToArray());

IEnumerable<T> myList;

string csv = String.Join(",", myList.Select(x => x.ToString()).ToArray());

.NET 4.0 was officially released. Now we can just say

IEnumerable<T> sequence;string csv = String.Join(",", sequence);

IEnumerable<string> can be converted into a string array very easily with LINQ (.NET 3.5):

IEnumerable<string> strings = ...;

string[] array = strings.ToArray();

It's easy enough to write the equivalent helper method if you need to:

public static T[] ToArray(IEnumerable<T> source)

{

    return new List<T>(source).ToArray();

}

Then call it like this:

IEnumerable<string> strings = ...;

string[] array = Helpers.ToArray(strings);

You can then call string.Join. Of course, you don't have to use a helper method:

// C# 3 and .NET 3.5 way:

string joined = string.Join(",", strings.ToArray());

// C# 2 and .NET 2.0 way:

string joined = string.Join(",", new List<string>(strings).ToArray());

The latter is a bit of a mouthful though :)

This is likely to be the simplest way to do it, and quite performant as well - there are other questions about exactly what the performance is like, including (but not limited to) this one.

Then you can just call the method on the original list:

string commaSeparated = myList.JoinStrings(", ");

You can create an extension method that you can call on any IEnumerable:

public static string JoinStrings<T>(

    this IEnumerable<T> values, string separator)

{

    var stringValues = values.Select(item =>

        (item == null ? string.Empty : item.ToString()));

    return string.Join(separator, stringValues.ToArray());

}

3.5, i was still able to do this. Its much more simpler and doesnt need lambda.
String.Join(",", myList.ToArray<string>());