Forum: Ruby <, >, and ranges in a case statement.

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Max W. (Guest)
on 2009-06-02 13:12
I feel like this should be simple but i can't figure it out.

In a case statement, i know how to use ranges to compare against the
given variable.  But how do i use < or > ?  eg i want to do this:

age = 25

category = case age
  when < 12 : "child"
  when 13..17 : "minor"
  when 18..24 : "young ad*lt"
  when 25..49 : "ad*lt"
  when 50..64 : "middle aged"
  when > 65   : "senior"
  else        : "not an age"
end

(please don't anybody be offended by my age categories, i just made up
this example off the top of my head)

Anyway, the above doesn't work - syntax error.
Neither does this:

when age < 12 : "child"

the test doesn't pass, so if age is eg 10, i get nil back.

Can someone set me straight?
thanks
max

*******************************
postscript - it seems the word 'ad*lt* triggers the spam filter.  hence
the odd wording above.
Brian C. (Guest)
on 2009-06-02 13:27
Max W. wrote:
> In a case statement, i know how to use ranges to compare against the
> given variable.  But how do i use < or > ?

Simplest solution is to use a Range with extreme bounds, or use an if
statement (if age < 25 ...).

The long answer is to explain that

  case foo
  when bar
    ...
  end

is syntactic sugar for

  if bar === foo
    ...
  end

So you can get whatever behaviour you like by creating an object which
responds to the === method.

class Bounds
  def initialize(meth,val)
    @meth, @val = meth, val
  end
  def ===(other)
    other.send(@meth, @val)
  end
end
def is(meth,val)
  Bounds.new(meth,val)
end

age = 70
case age
when is(:<,25)
  puts "Youngster"
when is(:>,65)
  puts "Oldie"
end

If you wanted this to be more efficient, you could define constants like

UNDER_25 = is(:<,25)
OVER_65 = is(:>,65)

case age
when UNDER_25
  ... etc
end
Robert K. (Guest)
on 2009-06-02 13:56
(Received via mailing list)
Attachment: cond.rb (0 Bytes)
2009/6/2 Brian C. <removed_email_address@domain.invalid>:
> Max W. wrote:
>> In a case statement, i know how to use ranges to compare against the
>> given variable.  But how do i use < or > ?

> end
> end
I've attached a similar but more general approach - and a few others as
well.

Kind regards

robert
Max W. (Guest)
on 2009-06-02 13:57
Wow, that's a lot more complicated than i thought.  I think for the sake
of ease and readability i'd stick with doing a more longwinded version,
like

category = case
  when age < 12               : "child"
  when (13..17).include? age  : "minor"
  when (18..24).include? age  : "young ad*lt"
  when (25..49).include? age  : "ad*lt"
  when (50..64).include? age  : "middle aged"
  when age > 65               : "senior"
  else                        : "not an age"
end

thanks for the insight though!

cheers
max
Max W. (Guest)
on 2009-06-02 14:01
thanks for your in-depth answer robert!  i'll chew over that.  but, in
terms of readability, i think my solution of not passing age into the
block and instead testing it on every line is fine.

thanks a lot though.
max
Brian C. (Guest)
on 2009-06-02 14:46
Max W. wrote:
> Wow, that's a lot more complicated than i thought.  I think for the sake
> of ease and readability i'd stick with doing a more longwinded version,
> like
>
> category = case
>   when age < 12               : "child"
>   when (13..17).include? age  : "minor"
>   when (18..24).include? age  : "young ad*lt"
>   when (25..49).include? age  : "ad*lt"
>   when (50..64).include? age  : "middle aged"
>   when age > 65               : "senior"
>   else                        : "not an age"
> end
>
> thanks for the insight though!

If you want to allow for the possibility of fractional ages:

  when (13...18).include? age
  when (18...25).include? age
  when (18...50).include? age
  .. etc
Max W. (Guest)
on 2009-06-02 14:53
Good point, thanks :)  i guess you meant (25..50) for the last one :)

cheers!
max
F. Senault (Guest)
on 2009-06-02 15:06
(Received via mailing list)
Le 2 juin 2009 à 11:12, Max W. a écrit :

> category = case age
>   when < 12 : "child"
>   when 13..17 : "minor"
>   when 18..24 : "young ad*lt"
>   when 25..49 : "ad*lt"
>   when 50..64 : "middle aged"
>   when > 65   : "senior"
>   else        : "not an age"
> end

As the others pointed out, there's no easy way to do what you want to.
On the other hand, if you know the bounds of your inputs, your method
isn't bad ; I'd write :

category = case age
  when  0...12  then "child"
  when 12...18  then "minor"
  when 18...25  then "young ad*lt"
  when 25...50  then "ad*lt"
  when 50...65  then "middle aged"
  when 65...999 then "senior"
  else               "not an age"
end

Note that the use of : within if's and case's has been deprecated in
Ruby 1.9 and the next versions.

Fred
Brian C. (Guest)
on 2009-06-02 15:51
Max W. wrote:
> Good point, thanks :)  i guess you meant (25..50) for the last one :)

Yeah, you can tell I copy-pasted it from the line above :-)
Clifford H. (Guest)
on 2009-06-02 17:27
(Received via mailing list)
Brian C. wrote:
> Simplest solution is to use a Range with extreme bounds,

... such as a range that ends in Infinity:

65..(1/0.0)
=> 65..Infinity

;-)

Clifford H..
Max W. (Guest)
on 2009-06-02 17:32
Clifford H. wrote:
> Brian C. wrote:
>> Simplest solution is to use a Range with extreme bounds,
>
> ... such as a range that ends in Infinity:
>
> 65..(1/0.0)
> => 65..Infinity
>
> ;-)
>
> Clifford H..
haha, i thought about that but it seemed kind of crazy.  It surprises me
a little that Infinity isn't a singleton class like NilClass in ruby.
Max W. (Guest)
on 2009-06-02 17:34
>> Brian C. wrote:

>> 65..(1/0.0)
>> => 65..Infinity

> haha, i thought about that but it seemed kind of crazy.  It surprises me
> a little that Infinity isn't a singleton class like NilClass in ruby.
Florian G. (Guest)
on 2009-06-02 17:48
(Received via mailing list)
On Jun 2, 2009, at 3:32 PM, Max W. wrote:

>>
>> Clifford H..
> haha, i thought about that but it seemed kind of crazy.  It
> surprises me
> a little that Infinity isn't a singleton class like NilClass in ruby.


I guess that is because there are actually 2 infinities and both are
valid
values with well-defined operations in IEEE754.

Regards,
Florian

--
Florian G.

smtp:   removed_email_address@domain.invalid
jabber: removed_email_address@domain.invalid
gpg:    533148E2
Mark T. (Guest)
on 2009-06-02 23:23
(Received via mailing list)
On Jun 2, 9:32 am, Max W. <removed_email_address@domain.invalid> wrote:
> Clifford H. wrote:
> > Brian C. wrote:
> >> Simplest solution is to use a Range with extreme bounds,
>
> > ... such as a range that ends in Infinity:
>
> > 65..(1/0.0)
> > => 65..Infinity

Interesting... you can assign it to a constant.

Infinity = 1/0.0

Then you can use it in ranges:

(-Infinity..0).include? 100000
=> false
(0..Infinity).include? 100000
=> true
Alex (Guest)
on 2009-06-02 23:27
(Received via mailing list)
That's an interesting idea.. I can see an opportunity for a great deal
of
abuse there, as well.
It would certainly be cool to write my infinite loops like:

(0..Infinity).each {|d| ... }


Alex
Max W. (Guest)
on 2009-06-03 01:29
By the way, this is a real good way to lock up your cpu, i just
discovered :)

infinity = 1.0/0
(0..infinity).to_a

grrrrrrriiiiiiinnnnnnnddddddddd
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