Question

I ve got a String array that I m wanting to add to a string builder by way of LINQ.

What I m basically trying to say is "For each item in this array, append a line to this StringBuilder".

I can do this quite easily using a foreach loop however the following code doesn t seem to do anything. What am I missing?

stringArray.Select(x => stringBuilder.AppendLine(x));

Where as this works:

foreach(String item in stringArray)
{
  stringBuilder.AppendLine(item);
}

Answer 1

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.

Answer 2

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

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

or

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

Answer 3

If you re using .NET core then this will work:

stringBuilder.AppendJoin(Environment.NewLine, stringArray);

Although it s not leveraging LINQ, but it does get it done in one line without adding any extra code.

Answer 4

stringArray.DoForAll(x => StringBuilder.AppendLine(x));

Where, DoForAll is an extension method:

public static class CommonExtensions 
{ 
    public static void DoForAll<T>(this IEnumerable<T> items, Action<T> action) where T: class 
    { 
        if (action == null) 
            throw new ArgumentNullException("action"); 
        foreach (var item in items) 
            action(item);   
    }
}

友情链接