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Aligning decimal numbers to the separator

October 20, 2009
http://www.iamraf.net/Samples/Aligning-decimal-numbers-to-the-separator

There are tons of options for custom formatting a number, but not enough :)

Let's take a series of double/decimal numbers:

   1: double[] doubles = {
   2:     -1234.56789,
   3:     1234.56789,
   4:     1234.5678,
   5:     1234.56,
   6:     1234.5,
   7:     1234.56789,
   8:     123.56789,
   9:     12.56789,
  10:     1.56789,
  11:     .56789,
  12:     -.56789,
  13: };

One classic way to format those numbers is the following:

   1: string fmt = "####0.0000";
   2: foreach(var d in doubles)
   3:     Console.WriteLine(d.ToString(fmt));

That unfortunately give this result:

   1: -1234,5679
   2: 1234,5679
   3: 1234,5678
   4: 1234,5600
   5: 1234,5000
   6: 1234,5679
   7: 123,5679
   8: 12,5679
   9: 1,5679
  10: 0,5679
  11: -0,5679

Since I needed to align the numbers in a diagnostic trace to the decimal separator, I wrote a little extension method that does the trick:

   1: public static class FormatHelper
   2: {
   3:     public static string ToStringAligned(this double d, string Format)
   4:     {
   5:         string t = d.ToString(Format);
   6:         if(Format.Length - t.Length < 0)
   7:             return t;
   8:         return string.Format("{0}{1}", new string(' ', Format.Length - t.Length), t);
   9:     }
  10:  
  11:     public static string ToStringAligned2(this double d, string Format)
  12:     {
  13:         return string.Format("{0," + Format.Length + ":" + Format + "}", d);
  14:     }
  15: }

Those two methods are equivalent. The second is shorter and probably the better. Since the syntax "{0,10:####0.0000}" still need to be parsed, maybe the second is not the faster. Should give a try under a stopwatch to have the answer. Furthermore with the first one I can choose the padding character. For example in a Html output the padding would be "&nbsp;".

The modified code to use this extension is as much as simple:

   1: foreach(var d in doubles)
   2:     Console.WriteLine(d.ToStringAligned(fmt));

And finally this is was I wanted to obtain:

   1: -1234,5679
   2:  1234,5679
   3:  1234,5678
   4:  1234,5600
   5:  1234,5000
   6:  1234,5679
   7:   123,5679
   8:    12,5679
   9:     1,5679
  10:     0,5679
  11:    -0,5679

Yes, no revolutions, nothing magic, but it just works.



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