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.

Answer 1

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

Answer 2

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();
}

Answer 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();