Re: Roman Numerals (Arrgh!)


On Nov 10, 2009, at 10:30 PM, Gennady Bystritsky wrote:
On Nov 10, 2009, at 6:43 PM, Rob Biedenharn wrote:
On Nov 10, 2009, at 8:49 PM, Gennady Bystritsky wrote:
On Nov 10, 2009, at 5:37 PM, Rob Biedenharn wrote:
On Nov 10, 2009, at 6:56 PM, Rick Barrett wrote:
I have a homework assignment where I have to convert an inputted
integer
into Roman Numerals. I was doing fine building upon the previous
steps

P.S. I saw Gennady's post, but I'd argue that no one would really
want
to solve the problem that way. And Nik's way doesn't give any help

Why not that way? It works and it is short ;-)

Gennady.

Not that it doesn't work, just that it might be easier/quicker to
rewrite than to understand. Short isn't *always* a virtue and if
there's a reason (performance?) to be terse, then there ought to be a
comment by way of explanation.

There are few truly necessary uses of Enumerable#inject and this
isn't

I respectfully disagree. inject() is a very powerful facility that
allows quick elegant implementation of many tasks at hand. I usually
start with an inject()-based implementation (where appropriate) and
then may refactor it later if performance is not satisfactory. The
latter does not happen very often, though. As for the virtue, the
less code you write the fewer bugs get in -- especially when you use
well tested standard facilities like inject().

Well, I won't argue the fact that inject is a powerful abstraction. I
*will* argue that it would be much easier to inject a bug (pun
intended ;-) into your original terse code than something that is a
bit longer, but tries to do less at each step. Changing/swapping array
subscripts, for example.


one of them, but if it were, I'd make it at least slightly more
readable:

def roman_numeral(number)
$numerals.inject(["", number]) { |(answer, number), (arabic,
roman)|

For that thanks a lot -- somehow I missed the fact it is possible in
ruby.

[ answer + roman * (number / arabic), number % arabic ]
}.first
end

And with an appropriately formed $numerals array, the "subtraction
rule" is already covered. ;-)

Would you please elaborate? You mean same algorithm and "better"
$numerals would cover mapping of 4 => "IV", 9 => "IX", etc.?


-Rob


Yes, that's it exactly. Testing/using 9 before 5, you find IX (and
stop) before you go to VIIII. You can't repeat one of the "subtraction
groups" the way that you can repeat the individual numerals: 8 is
always VIII and never IVIV or IIX

Rob Biedenharn http://agileconsultingllc.com
Rob@xxxxxxxxxxxxxxxxxxxxxx




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