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From: Robert Klemme on 21 Jul 2010 06:55
2010/7/21 Xavier Noria <fxn(a)hashref.com>:
> On Wed, Jul 21, 2010 at 12:12 PM, Tom Ha <tom999(a)gmx.net> wrote:
>
>> what's the most simple solution in Ruby to check if value x is a
>> multiple of y?
>
> That's typically done with the modulus operator, Active Support
> defines it this way
>
>    class Integer
>      # Check whether the integer is evenly divisible by the argument.
>      def multiple_of?(number)
>        number != 0 ? self % number == 0 : zero?
>      end
>    end
>
> It is special-cased because you can't do modulus 0.

I see a benchmark lurking: that version vs. this one.

class Integer
def multiple_off? number
zero? || self % number == 0
end
end

:-)

Don't have the time right now...

Cheers

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

From: Joseph E. Savard on 21 Jul 2010 10:26

x = 9
y = 3

puts "yep" if (x%y).zero?

x = 9
y = 2

puts "nope" if !(x%y).zero?

> From: Tom Ha <tom999(a)gmx.net>
> Reply-To: <ruby-talk(a)ruby-lang.org>
> Newsgroups: comp.lang.ruby
> Date: Wed, 21 Jul 2010 19:12:30 +0900
> To: ruby-talk ML <ruby-talk(a)ruby-lang.org>
> Subject: How to check if x is a multiple of y
>
> Hi there,
>
> what's the most simple solution in Ruby to check if value x is a
> multiple of y?
>
> "if x/y.integer?"
>
> ...is obviously not the solution.
>
> Thanks a lot!
> Tom
> --
> Posted via http://www.ruby-forum.com/.
>


From: Robert Klemme on 21 Jul 2010 13:43
On 21.07.2010 13:20, Xavier Noria wrote:
> On Wednesday, July 21, 2010, Robert Klemme<shortcutter(a)googlemail.com> wrote:
>> 2010/7/21 Xavier Noria<fxn(a)hashref.com>:
>>> On Wed, Jul 21, 2010 at 12:12 PM, Tom Ha<tom999(a)gmx.net> wrote:
>>>
>>>> what's the most simple solution in Ruby to check if value x is a
>>>> multiple of y?
>>>
>>> That's typically done with the modulus operator, Active Support
>>> defines it this way
>>>
>>> class Integer
>>> # Check whether the integer is evenly divisible by the argument.
>>> def multiple_of?(number)
>>> number != 0 ? self % number == 0 : zero?
>>> end
>>> end
>>>
>>> It is special-cased because you can't do modulus 0.
>>
>> I see a benchmark lurking: that version vs. this one.
>>
>> class Integer
>> def multiple_off? number
>> zero? || self % number == 0
>> end
>> end
>>
>> :-)
>
> But that one is not well-defined for 1.multiple_of?(0) :-)

There you see why posting in a hurry is a bad idea. Thanks for catching
that.

Cheers

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/
From: Colin Bartlett on 21 Jul 2010 14:49
[Note: parts of this message were removed to make it a legal post.]

On Wed, Jul 21, 2010 at 6:45 PM, Robert Klemme
<shortcutter(a)googlemail.com>wrote:

> On 21.07.2010 13:20, Xavier Noria wrote:
>
>> On Wednesday, July 21, 2010, Robert Klemme<shortcutter(a)googlemail.com>
>> wrote:
>>
>>> ...
>>
>> I see a benchmark lurking: that version vs. this one.
>>> class Integer
>>> def multiple_off? number
>>> zero? || self % number == 0
>>> end
>>> end
>>>
>>> :-)
>>
>>
>> But that one is not well-defined for 1.multiple_of?(0) :-)
>>
>
> There you see why posting in a hurry is a bad idea. Thanks for catching
> that.

For what they are worth (which is very little as I distrust benchmarks which
haven't been run sufficiently many times to generate reliable standard
deviations, not to mention my Windows Vista installation doing even more
apparently random and purposeless disk i/o than usual) these benchmarks
suggest that (ignoring the minor bug!) multiple_off? was usually slightly
slower than multiple_of? on my system about two hours ago!

ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-mingw32]
each benchmark is a 1_000_0000.times run;

user system total real

num= 72 denom= 13

multiple_of? 0.921000 0.000000 0.921000 ( 1.012000)
multiple_off? 0.967000 0.000000 0.967000 ( 1.177000)

multiple_of? 0.827000 0.015000 0.842000 ( 0.992000)
multiple_off? 0.983000 0.000000 0.983000 ( 1.110000)

num= 72 denom= 12

multiple_of? 0.874000 0.000000 0.874000 ( 1.072000)
multiple_off? 0.967000 0.000000 0.967000 ( 1.182000)

multiple_of? 0.936000 0.000000 0.936000 ( 1.090000)
multiple_off? 1.030000 0.000000 1.030000 ( 1.156000)

num= 0 denom= 0

multiple_of? 0.874000 0.000000 0.874000 ( 1.108000)
multiple_off? 0.780000 0.000000 0.780000 ( 1.004000)

multiple_of? 0.827000 0.000000 0.827000 ( 1.122000)
multiple_off? 0.889000 0.000000 0.889000 ( 1.043000)

num= 72 denom= 0

multiple_of? 0.905000 0.000000 0.905000 ( 1.114000)
multiple_of? 0.936000 0.000000 0.936000 ( 1.088000)

multiple_off?
#<ZeroDivisionError: divided by 0>

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