Forum: Ruby Calculating roman numerals

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Shiloh M. (Guest)
on 2007-01-02 23:36
(Received via mailing list)
Ok, I'm having trouble with another exercise in this book. It has
asked me to write a program that will calculate the old school roman
numeral value for a given modern number (up to the thousands). To
clarify, old school roman numerals didn't do the subtraction thing, so
4 is IIII, nine is VIIII, etc. I've played around with a few options
using division, loops and modulus, but can't seem to get my brain
around the problem...any suggestions?

Shiloh
Carlos (Guest)
on 2007-01-02 23:44
(Received via mailing list)
[Shiloh M. <removed_email_address@domain.invalid>, 2007-01-02 22.35 CET]
> Ok, I'm having trouble with another exercise in this book. It has
> asked me to write a program that will calculate the old school roman
> numeral value for a given modern number (up to the thousands). To
> clarify, old school roman numerals didn't do the subtraction thing, so
> 4 is IIII, nine is VIIII, etc. I've played around with a few options
> using division, loops and modulus, but can't seem to get my brain
> around the problem...any suggestions?

A hint: Try loops and subtractions.

Good luck.
Shiloh M. (Guest)
on 2007-01-02 23:58
(Received via mailing list)
Thank you. That gave me an entirely new way to look at this. I am
working on one solution now, but I will try that next. If they both
work I'll post both as I am curious which will be more efficient.
William J. (Guest)
on 2007-01-03 00:30
(Received via mailing list)
Shiloh M. wrote:
> --
> It is better to rule in hell than serve in heaven.

class Integer
  def to_roman
    "I =1       V =5      X = 10       L = 50
    C = 100    D = 500   M = 1000".
    scan( / ([A-Z]) \s *= \s* (\d+) /x ).
    map{|letter,val|  [ letter, val.to_i ] }.
    sort_by{|a| -a.last}.
    inject( [ "", self ] ){|roman, pair|
      [ roman.first + pair.first * (roman.last / pair.last),
        roman.last % pair.last ] }.
    first
  end
end
Gregory S. (Guest)
on 2007-01-03 14:46
(Received via mailing list)
On Wed, Jan 03, 2007 at 06:35:02AM +0900, Shiloh M. wrote:
} Ok, I'm having trouble with another exercise in this book. It has
} asked me to write a program that will calculate the old school roman
} numeral value for a given modern number (up to the thousands). To
} clarify, old school roman numerals didn't do the subtraction thing, so
} 4 is IIII, nine is VIIII, etc. I've played around with a few options
} using division, loops and modulus, but can't seem to get my brain
} around the problem...any suggestions?

We recently had a golfing competition at work on going the other
direction
(i.e. roman numeral to arabic). Our best solution:

def x s
  p=t=0
  s.scan(/./){|r|
    i=' IVXLCDM'.index r
      c=10**(i/2)/(2-i%2)
      t+= p<c ?-p:p
      p=c
  }
  t+p
end

} Shiloh
--Greg
William J. (Guest)
on 2007-01-04 14:36
(Received via mailing list)
Gregory S. wrote:
> (i.e. roman numeral to arabic). Our best solution:
> end
>
> } Shiloh
> --Greg

Another way:

require 'enumerator'
def y s
  t=0
  (s.split("").map{|c|
    n=' IVXLCDM'.index c;10**(n/2)/(2-n%2)}<<0).
  each_cons(2){|a,b| t+= a<b ?-a:a}
  t
end
Rodrigo B. (Guest)
on 2007-01-05 01:54
There was a related ruby quiz:

 http://rubyquiz.com/quiz22.html

-rb.
Jason B. (Guest)
on 2007-01-05 04:58
Shiloh M. wrote:
> Ok, I'm having trouble with another exercise in this book. It has


Which book?

JB
Jan S. (Guest)
on 2007-01-06 20:30
(Received via mailing list)
On 1/2/07, Shiloh M. <removed_email_address@domain.invalid> wrote:
> Ok, I'm having trouble with another exercise in this book. It has
> asked me to write a program that will calculate the old school roman
> numeral value for a given modern number (up to the thousands). To
> clarify, old school roman numerals didn't do the subtraction thing, so
> 4 is IIII, nine is VIIII, etc. I've played around with a few options
> using division, loops and modulus, but can't seem to get my brain
> around the problem...any suggestions?
>
> Shiloh

Look for older thread "Need help with a program".
Tim P. (Guest)
on 2007-01-06 20:31
(Received via mailing list)
On 1/2/07, Shiloh M. <removed_email_address@domain.invalid> wrote:
> Ok, I'm having trouble with another exercise in this book. It has
> asked me to write a program that will calculate the old school roman
> numeral value for a given modern number (up to the thousands). To
> clarify, old school roman numerals didn't do the subtraction thing, so
> 4 is IIII, nine is VIIII, etc. I've played around with a few options
> using division, loops and modulus, but can't seem to get my brain
> around the problem...any suggestions?
>

Lest we all forget about the code snippets on RubyForge ...

http://rubyforge.org/snippet/detail.php?type=snipp...

Should do all you need (and more)

Blessings,
TwP
Gerald E. (Guest)
on 2007-01-08 09:25
(Received via mailing list)
On Wed, 03 Jan 2007 06:35:02 +0900, Shiloh M. wrote:

> Ok, I'm having trouble with another exercise in this book. It has
> asked me to write a program that will calculate the old school roman
> numeral value for a given modern number (up to the thousands). To
> clarify, old school roman numerals didn't do the subtraction thing, so
> 4 is IIII, nine is VIIII, etc. I've played around with a few options
> using division, loops and modulus, but can't seem to get my brain
> around the problem...any suggestions?
>
> Shiloh

Many people have answered, but since I'm a beginner I would like to have
some comments on the following. Which I think is pretty ruby-esque

ans=0
roman="XVIII"
{"X"=>10,"V"=>5,"I"=>1}.each_pair do |letter,
number|ans+=roman.count(letter)*number end;ans


Kind regards,
Gerald
William J. (Guest)
on 2007-01-08 09:45
(Received via mailing list)
Gerald E. wrote:
> > Shiloh
> Gerald
The original poster asked for a way to translate from modern numerals
to roman numerals.  You're doing the opposite.

Your method will convert old-school roman numerals, but it
won't work for "XIV".
Gregory B. (Guest)
on 2007-01-19 17:30
(Received via mailing list)
On 1/4/07, Tim P. <removed_email_address@domain.invalid> wrote:

> Lest we all forget about the code snippets on RubyForge ...

The code snippets thing is super cool, if only it was better
organized.  Not sure if we can do much with it, since it's mostly up
to GForge...

I just wish it was easier to navigate, search, etc.
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