LINQ to append to a StringBuilder from a String[]

If you insist on doing it in a LINQy way:

StringBuilder builder = StringArray.Aggregate(
                            new StringBuilder(),
                            (sb, s) => sb.AppendLine(s)
                        );

Alternatively, as Luke pointed out in a comment on another post, you could say

Array.ForEach(StringArray, s => stringBuilder.AppendLine(s));

The reason that Select does not work is because Select is for projecting and creating an IEnumerable of the projection. So the line of code

StringArray.Select(s => stringBuilder.AppendLine(s))

does not iterate over the StringArray calling stringBuilder.AppendLine(s) on each iteration. Rather, it creates an IEnumerable<StringBuilder> that can be enumerated over.

I suppose that you could say

var e = stringArray.Select(x => stringBuilder.AppendLine(x));
StringBuilder sb = e.Last();
Console.WriteLine(sb.ToString());

but that is really hideous.

Use the "ForEach" extension method instead of "Select".

stringArray.ToList().ForEach(x => stringBuilder.AppendLine(x));

or

Array.ForEach(stringArray, x => stringBuilder.AppendLine(x));