What's the most efficient way to format the following string?

Question

I have a very simple question, and I shouldn't be hung up on this, but I am. Haha!

I have a string that I receive in the following format(s):

123

123456-D53

123455-4D

234234-4

123415

The desired output, post formatting, is:

123-455-444

123-455-55

123-455-5

or

123-455

The format is ultimately dependent upon the total number of characters in the original string..

I have several ideas of how to do this, but I keep thing there's a better way than string.Replace and concatenate...

Thanks for the suggestions..

Ian

Answer 1

EDIT: See history for old versions.
You could use char.IsDigit() for finding digits, only.

var output = new StringBuilder();
var digitCount = 0;

foreach( var c in input )
{
  if( char.IsDigit( c ) )
  {
    output.Append( c );
    digitCount++;
    if( digitCount % 3 == 0 )
    {
      output.Append( "-" );
    }
  }
}

// Remove possible last -
return output.ToString().TrimEnd('-');

This code should fill from left to right (now I got it, first read, then code) ...
Sorry, I still can't test this right now.

Answer 2

I assume this does not merely rely upon the inputs always being numeric? If so, I'm thinking of something like this

private string ApplyCustomFormat(string input)
{
    StringBuilder builder = new StringBuilder(input.Replace("-", ""));

    int index = 3;
    while (index < builder.Length)
    {
        builder.Insert(index, "-");
        index += 4;
    }
    return builder.ToString();
}

Answer 3

Tanascius is right but I cant comment or upvote due to my lack of rep but if you want additional info on the string.format Ive found this helpful. http://blog.stevex.net/string-formatting-in-csharp/

Answer 4

Not the fastest, but easy on the eyes (ed: to read):

string Normalize(string value)
{
    if (String.IsNullOrEmpty(value)) return value;

    int appended = 0;
    var builder = new StringBuilder(value.Length + value.Length/3);
    for (int ii = 0; ii < value.Length; ++ii)
    {
        if (Char.IsLetterOrDigit(value[ii]))
        {
            builder.Append(value[ii]);
            if ((++appended % 3) == 0) builder.Append('-');
        }
    }

    return builder.ToString().TrimEnd('-');
}

Uses a guess to pre-allocate the StringBuilder's length. This will accept any Alphanumeric input with any amount of junk being added by the user, including excess whitespace.

Answer 5

Here's a method that uses a combination of regular expressions and LINQ to extract groups of three letters at a time and then joins them together again. Note: it assumes that the input has already been validated. The validation can also be done with a regular expression.

string s = "123456-D53";
string[] groups = Regex.Matches(s, @"\w{1,3}")
                       .Cast<Match>()
                       .Select(match => match.Value)
                       .ToArray();
string result = string.Join("-", groups);

Result:

123-456-D53