From: Colin Bartlett <colinb2r@...>
Date: 2010-07-20T23:31:00+09:00
Subject: Re: How do I format return this value?

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On Tue, Jul 20, 2010 at 1:13 PM, Chad Weier <emily.ward89@gmail.com> wrote:

> ...

What would be the neatest and cleanest way to convert them to a
> formatted value like this (note the rounding also)
>   valuea - 100.00 valueb - 555,555.56
> I've found lots of code that does bit and pieces like I need but not
> anything that does commas and rounding to 2 decimal places.

The following methods (for Integers and Floats) are cut down versions of
some more general number formatting methods I wrote for myself some time
ago. No guarantees that they do what you want, but some quick tests seem to
show they do.

class Integer
   # Puts digit separators for each group of 3 digits,
   # with option to use a separator which is not an underscore.
  def to_s!( grp_sep = '_' )
    s = self.to_s
    if grp_sep then
      n = s.length
      ne = ( if self < 0 then 1 else 0 end )
      while (n -= 3) > ne do; s[ n, 0 ] = grp_sep; end
    end
    s
  end
end

class Float
   # Puts integer part digit separators for each group of 3 digits,
   # with option to use a separator which is not an underscore.
   # (if "." is used as the digits separator then the "decimal separator"
   #  will be changed from "." to ",");
  def to_s!( n_dec_places, grp_sep = '_' )
    unless n_dec_places.kind_of?( Integer ) then
      raise "Float#to_s! - number of decimal places must be an integer"
    end
    unless n_dec_places >= 0 then
      raise "Float#to_s! - negative number of decimal places yet to be
implemented to give robust results"
    end
    fmt_str = "%.#{n_dec_places}f"
    s = sprintf( fmt_str, self )
    if grp_sep then
      n = s.rindex( '.' )  # if n_dec_places == 0 then n = nil
      s[n, 1] = ','  if n && grp_sep == '.'
      n ||= s.length
      ne = ( if self < 0 then 1 else 0 end )
      while (n -= 3) > ne do; s[ n, 0 ] = grp_sep; end
    end
    s
  end
end

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