How to append Hyphens to a string at each nth position?

Question

I am getting strings like "123456", "abcdef", "123abc" from another application. I need to format the strings like "123-456","abc-def", "123-abc". The length of the strings can also vary like we can have a string of lenght 30 char. If the 3rd position is chosen then after every 3rd character a hyphen should be inserted.

ex: input "abcdxy123z" output "abc-dxy-123-z" for 3rd position.

if we choose 2nd position then output will be

"ab-cd-xy-12-3z"

I tried with String.Format("{0:####-####-####-####}", Convert.ToInt64("1234567891234567")) but if I get a alphanumeric string, it does not work.

Welcome to StackOverflow. You need to provide us with exact details of what you're trying to achieve, and if possible the code that you have already tried. It is very unclear what you need, as you have given us 3 examples - all 6 characters in length - told us that the number of character could vary, but NOT told us what format those should take — freefaller, Jan 29 '14 at 17:12
The position can vary and the hyphen will repeat on every third position. ex for 123456789012 it will be 123-456-789-012 like this — user2943892, Jan 29 '14 at 17:14
OK, so update your question (by **editing** not commenting), give as MUCH *relevant* information as you can. Then the "on hold" status might be removed — freefaller, Jan 29 '14 at 17:15
Actually it's "as much information" **and the code** you're having problem with. — Pierre-Luc Pineault, Jan 29 '14 at 17:15
My problem is that if use string.Format with #, then it works only for numerics. — user2943892, Jan 29 '14 at 17:15
You can edit your question directly, you do not need to comment. — Pierre-Luc Pineault, Jan 29 '14 at 17:16
So, the question is how to convert a string, inserting a hyphen at each nth position. — Polyfun, Jan 29 '14 at 17:23
I don't see why a reopen is warranted. Please edit your post with your attempts so far; it is a prerequisite instead of just giving us a list of requirements. — Jeroen Vannevel, Jan 29 '14 at 17:29
This could be easily done in PHP with `chunk_split` and `implode`. `chunk_split` equivalent: http://stackoverflow.com/questions/1450774/splitting-a-string-into-chunks-of-a-certain-size `implode` equivalent: http://stackoverflow.com/questions/7598826/alternative-of-phps-explode-implode-functions-in-c-sharp — Brilliand, Jan 29 '14 at 17:39
@Hogan Probably no change, judging by his "second position" example . — Brilliand, Jan 29 '14 at 17:44
And don't forget to accept the answer which you would prefer — Fedor, Jan 29 '14 at 17:59

p.s.w.g · Answer 1 · 2014-01-29T18:03:15.847

You could use a little bit of Linq, like this:

string Hyphenate(string str, int pos) {
    return String.Join("-",
        str.Select((c, i) => new { c, i })
           .GroupBy(x => x.i / pos)
           .Select(g => String.Join("", g.Select(x => x.c))));
}

Or like this:

string Hyphenate(string str, int pos) {
    return String.Join("-",
        Enumerable.Range(0, (str.Length - 1) / pos + 1)
            .Select(i => str.Substring(i * pos, Math.Min(str.Length - i * pos, pos))));
}

Or you could use a regular expression, like this:

string Hyphenate(string str, int pos) {
    return String.Join("-", Regex.Split(str, @"(.{" + pos + "})")
                                 .Where(s => s.Length > 0));
}

Or like this:

string Hyphenate(string str, int pos) {
    return String.Join("-", Regex.Split(str, @"(?<=\G.{" + pos + "})(?!$)"));
}

All of these methods will return the same result:

Console.WriteLine(Hyphenate("abcdxy123z", 2)); // ab-cd-xy-12-3z
Console.WriteLine(Hyphenate("abcdxy123z", 3)); // abc-dxy-123-z
Console.WriteLine(Hyphenate("abcdxy123z", 4)); // abcd-xy12-3z

Hogan · Answer 2 · 2014-01-29T17:56:33.170

5

The power of the for statement:

string str = "12345667889";
int loc = 3;

for(int ins=loc; ins < str.Length; ins+=loc+1)
   str = str.Insert(ins,"-");

Gives 123-456-678-89

As a function:

string dashIt(string str,int loc)
{
  if (loc < 1) return str;

  StringBuilder work = new StringBuilder(str);

  for(int ins=loc; ins < work.Length; ins+=loc+1)
     work.Insert(ins,"-");

  return work.ToString();
}

edited Jan 29 '14 at 17:56

answered Jan 29 '14 at 17:47

Hogan

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10
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+1 for the second version, but your first code part uses `String.Insert` which returns _new_ string each call – Fedor Jan 29 '14 at 18:15
@Fyodor - true, the first one was done quickly to show how to do it with a for statement. As a side note, the Linq answers by p.s.w.g create as many or more strings as my first code example. – Hogan Jan 29 '14 at 19:27
Sure! I like it's brevity too, nice example, just noted that the second one is slightly different and get confused a little. – Fedor Jan 29 '14 at 19:46
@Fyodor - I could have used the same code as the first one in the 2nd example but the pass by reference vs pass by value issues would have made the code hard to understand for new coders... I felt this was clearer since it looked like what it did. – Hogan Jan 29 '14 at 20:42

score 3 · Answer 3 · answered Jan 29 '14 at 17:40

3

With StringBuilder:

string input = "12345678"; //could be any length
int position = 3; //could be any other number
StringBuilder sb = new StringBuilder();

for (int i = 0; i < input.Length; i++)
{
    if (i % position == 0){
        sb.Append('-');
    }
    sb.Append(input[i]);
}
string formattedString = sb.ToString();

answered Jan 29 '14 at 17:40

Zzyrk

907
8
16

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Much faster to increment by position, don't you think? – Hogan Jan 29 '14 at 17:58
@Hogan You are right it would be faster. But I didnt know of the Insert method. Guess I learned sometinhg too XD – Zzyrk Jan 29 '14 at 18:06
Substring would let you do it without insert. – Hogan Jan 30 '14 at 15:07

How to append Hyphens to a string at each nth position?

3 Answers3