LINQ to append to a StringBuilder from a String[]

问题

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);
}

回答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.

回答2:

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

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

回答3:

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);   
    }
}

来源：https://stackoverflow.com/questions/1708247/linq-to-append-to-a-stringbuilder-from-a-string

标签

linq

lambda

stringbuilder