Convert 125% into 1.25?

ruby-talk
1

irb(main):011:0> format("%.2f",125)
=> "125.00"
irb(main):012:0> format("%.2f",125%)
SyntaxError: compile error
(irb):12: syntax error, unexpected ')'

···

--
Posted via http://www.ruby-forum.com/.

2

From a mathematical aspect the % sign means 1/100 so 125 % equals
1.25.

Pen Ttt schrieb (am 21.8.10 07:16):

irb(main):011:0> format("%.2f",125)
=> "125.00"

irb(main):012:0> format("%.2f",125%)
SyntaxError: compile error
(irb):12: syntax error, unexpected ')'

Ruby does not allow you to write 125% like that.
You can however divide 125 by 100 (or rather 100.0 to get a
floating point number):

format( "%.2f", 125 / 100.0 )
=> "1.25"

Regards,
  Philipp

3

Pen,

···

On Saturday 21 August 2010, Pen Ttt <myocean135@yahoo.cn> wrote:

irb(main):012:0> format("%.2f",125%)

125% is, strictly spoken, not a number, but a number plus a unit. The unit
is a character, not an integer, and this makes "125%" only valid as a string
in Ruby. You've got to remove the "%" sign before you can treat "125" as a
number.

HTH.

      Eric

4

You can sort of cheat, thanks to Rubys open classes.
Just add a method to Fixnum:

~:) irb

?> 100.class
=> Fixnum

?> class Fixnum

  def percent
    return self.to_f / 100
  end
end

=> nil

?> 100.percent
=> 1.0

125.percent

=> 1.25

quit

~:)

This is pretty evil, though :slight_smile:

It is actually possible to define a method called '%', but then you have
to call it as

100.%()

which looks awful.

···

On Sat, Aug 21, 2010 at 1:58 PM, Eric MSP Veith <eveith@wwweb-library.net> wrote:

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Pen,

On Saturday 21 August 2010, Pen Ttt <myocean135@yahoo.cn> wrote:

irb(main):012:0> format("%.2f",125%)

125% is, strictly spoken, not a number, but a number plus a unit. The unit
is a character, not an integer, and this makes "125%" only valid as a string
in Ruby. You've got to remove the "%" sign before you can treat "125" as a
number.

HTH.

                   Eric

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5

?> class Fixnum

def percent

the appropriate place to put that is Integer, not Fixnum.

···

On Aug 22, 2010, at 13:32 , Dick Davies wrote:

% ruby -e 'p 100.class.superclass'
Integer

6

?> class Fixnum

def percent

the appropriate place to put that is Integer, not Fixnum.

% ruby -e 'p 100.class.superclass'
Integer

Or even Numeric:

1.class.ancestors

=> [Fixnum, Integer, Numeric, Comparable, Object, Kernel, BasicObject]

class Numeric
  def percent
    self.to_f / 100.0
    end
  end

=> nil

5.percent

=> 0.05

125.percent

=> 1.25

14.7.percent

=> 0.147

(99+"44/100".to_r).percent

=> 0.9944

-Rob

Rob Biedenharn
Rob@AgileConsultingLLC.com http://AgileConsultingLLC.com/
rab@GaslightSoftware.com http://GaslightSoftware.com/

···

On Aug 22, 2010, at 7:59 PM, Ryan Davis wrote:

On Aug 22, 2010, at 13:32 , Dick Davies wrote:

7

Ah, good catch both, thanks.

···

On Mon, Aug 23, 2010 at 2:02 AM, Rob Biedenharn <Rob@agileconsultingllc.com> wrote:

On Aug 22, 2010, at 7:59 PM, Ryan Davis wrote:

On Aug 22, 2010, at 13:32 , Dick Davies wrote:

?> class Fixnum

def percent

the appropriate place to put that is Integer, not Fixnum.

% ruby -e 'p 100.class.superclass'
Integer

Or even Numeric:

> 1.class.ancestors
=> [Fixnum, Integer, Numeric, Comparable, Object, Kernel, BasicObject]
> class Numeric
> def percent
> self.to_f / 100.0
> end
> end
=> nil
> 5.percent
=> 0.05
> 125.percent
=> 1.25
> 14.7.percent
=> 0.147
> (99+"44/100".to_r).percent
=> 0.9944

8

I said Integer because of how the original problem was described. I thought about floats and decided quickly that it didn't make sense... but looking at your examples above, that actually works and reads pretty well.

···

On Aug 22, 2010, at 18:02 , Rob Biedenharn wrote:

Or even Numeric:

> 1.class.ancestors
=> [Fixnum, Integer, Numeric, Comparable, Object, Kernel, BasicObject]
> class Numeric
> def percent
> self.to_f / 100.0
> end
> end
=> nil
> 5.percent
=> 0.05
> 125.percent
=> 1.25
> 14.7.percent
=> 0.147
> (99+"44/100".to_r).percent
=> 0.9944

9

> Or even Numeric:
> > class Numeric
> > def percent
> > self.to_f / 100.0
> > end
> > end
> ...

I said Integer because of how the original problem was described. I thought

about floats and decided quickly that it didn't make sense... but looking at
your examples above, that actually works and reads pretty well.

As a suggestion, if Rational is being used maybe "override" that with the
following to avoid rounding differences: typically interest rates as
percentages have the fractional part as 1/2, 3/4, 5/8, etc, so mostly do get
"mapped" to "precise" floats, but there might be uses of 2/5, etc
class Rational
  def percent; self / 100; end
end
class Integer
  def percent; Rational( self, 100); end
end

···

On Mon, Aug 23, 2010 at 8:22 AM, Ryan Davis <ryand-ruby@zenspider.com>wrote:

On Aug 22, 2010, at 18:02 , Rob Biedenharn wrote: