From: Rick DeNatale <rick.denatale@...>
Date: 2007-05-03T08:06:13+09:00
Subject: Re: Inverse scanf: finding format specifers of existing fields

On 5/2/07, Bil Kleb <Bil.Kleb@nasa.gov> wrote:
> Hi,
>
> I have files full of numbers that I need to twiddle,
> but the format of the numbers cannot change[1], e.g.,
>
>   '0.4577' -> '0.7728'
>
> or
>
> '-2.345e-02' -> ' 1.232e-03'
>
> Using scanf for the output seems to be the solution to
> the second half of the problem, but how does one derive
> the format specifier string of the input fields, which vary?
>
Bill,

How's this for a start?  I wrote it leaning towards clarity vs. conciseness.

rick@frodo:/public/rubyscripts$ cat number_format.rb
class String
  def to_number_format
    m = match(%r{^([ ]*)([+-]?)(.*)$})
    leading_blanks, sign, rest = m[1], m[2], m[3]
    plus_flag = sign == '+' ? sign : ''
    case rest
    when %r{^([\d]\.([\d]+)([eE])[+-][\d]+)(.*)$}
      # exponentiated float
      entirety, frac_part, e_or_E, exponent, suffix = $1, $2, $3, $4, $5
      entirety = leading_blanks << entirety
      "%#{entirety.length}.#{frac_part.length}#{e_or_E}#{suffix}"
    when %r{^([\d]+\.([\d]*))(.*)$}
      # simple float
      entirety, frac_part, suffix = $1, $2, $3
      zero = frac_part.match(/00$/) ? '0' : ''
      "%#{zero}#{entirety.length}.#{frac_part.length}f#{suffix}"
    when %r{^(0[\d]+)([^e.]*)$}
      # zero padded integer
      digits, suffix = $1, $2
      "#{leading_blanks}%#{plus_flag}0#{digits.length}d#{$suffix}"
    when %r{^([\d]+)([^e.]*)$}
      # whitespace padded integer
      digits, suffix = $1, $2
      digits = leading_blanks << digits
      "%#{digits.length}d#{suffix}"
   else
      nil
    end
  end
end

x = '0.4577'
puts x
puts x.to_number_format
puts x.to_number_format % x.to_f
puts(x.to_number_format % 0.7728)
puts (x.to_number_format % x.to_f) == x
puts

x = '-2.345e-02'
puts x
puts x.to_number_format
puts(x.to_number_format % x.to_f)
puts(x.to_number_format % 1.232e-03)
puts (x.to_number_format % x.to_f) == x
puts


x = '12345'
puts x
puts x.to_number_format
puts(x.to_number_format % x.to_i)
puts(x.to_number_format % 765)
puts (x.to_number_format % x.to_f) == x
puts

x = '  00012345'
puts x
puts x.to_number_format
puts(x.to_number_format % x.to_i)
puts(x.to_number_format % 765)
puts (x.to_number_format % x.to_i) == x
puts

x = '  12345'
puts x
puts x.to_number_format
puts(x.to_number_format % x.to_i)
puts(x.to_number_format % 765)
puts (x.to_number_format % x.to_i) == x

rick@frodo:/public/rubyscripts$ ruby number_format.rb
0.4577
%6.4f
0.4577
0.7728
true

-2.345e-02
%9.3e
-2.345e-02
1.232e-03
true

12345
%5d
12345
  765
true

  00012345
  %08d
  00012345
  00000765
true

  12345
%7d
  12345
    765
true


-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/