Styjun

I'd like to modify a source string which is looking like

"one.two.three" 

and transfer it into a string with slashes to use it as a folder string which has the following structure:

"oneone.twoone.two.three"

Do you know more elegant ways to realize this, than my solution below? I'm not very satisfied with my for-loops.

var folder = "one.two.three";
var folderParts = folder.Split('.');
var newFolder = new StringBuilder();
for (int i = 0; i < folderParts.Length; i++)

 for (int j = 0; j < i; j++)
 
 if (j == 0)
 
 newFolder.Append("\");
 

 newFolder.Append($"folderParts[j].");
 

 newFolder.Append(folderParts[i]);

You can do this quite tersely with Regex

var newFolder = Regex.Replace(folder, @".", @"$`.");

This matches on each period. Each time it finds a period, it inserts a backslash and then the entire input string before the match ($`). We have to add the period in again at the end.

So, steps are (< and > indicate text inserted by the substitution at that step):

1. Match on the 1st period. one<one>.two.three
   


2. Match on the 2nd period. oneone.two<one.two>.three
   


3. Result: oneone.twoone.two.three
   

For bonus points, use Path.DirectorySeparatorChar for cross-platform correctness.

var newFolder = Regex.Replace(folder, @".", $"Path.DirectorySeparatorChar$`.")

Here's another linqy way:

var a = "";
var newFolder = Path.Combine(folder.Split('.')
 .Select(x => a += (a == "" ? "" : ".") + x).ToArray());

You can try Linq:

 string folder = "one.two.three";
 string[] parts = folder.Split('.');

 string result = Path.Combine(Enumerable
 .Range(1, parts.Length)
 .Select(i => string.Join(".", parts.Take(i)))
 .ToArray());

 Console.Write(newFolder);

Outcome:

 oneone.twoone.two.three 

You can go forward-only in one loop like this:

 var folder = "one.two.three";
 var newFolder = new StringBuilder();

 int index = -1;
 while (index + 1 < folder.Length) 
 index = folder.IndexOf('.', index + 1);
 if (index < 0) 
 newFolder.Append(folder);
 break;
 
 else 
 newFolder.Append(folder, 0, index);
 newFolder.Append(Path.DirectorySeparatorChar);
 
 

You can try it out here.

Instead of splitting the string first, I find it more elegant to start with what you have and reduce it:

var folder = "one.two.three";
var newFolder = string.Empty;
for (var f = folder; f.Any(); f = f.Remove(Math.Max(f.LastIndexOf('.'), 0)))
 newFolder = Path.Combine(f, newFolder);

Console.WriteLine(newFolder);

Output:

oneone.twoone.two.three