Rails - Mar 2011 - why does my method return an error if argument is not a number?

Hey all,

I get the following error message:
ActionView::TemplateError (class or module required for rescue clause)
in app/vie$ app/helpers/format_helper.rb:116:in `divide_numbers''


Basically I have a field in database called Student Fails and I populate
fields with data. Sometimes the value can be empty - not null, not
integer, just empty because when user updates record they clear out
field and update it. First in my progressbar file I render a partial
called progressbar_item, passing in the string to the partial in render
method as well as data parameters that I can use in my progressbar file:


      = render "dashboard/progressbar_item.html", :actual =>
@student_counters[:student_failed], :expected =>
cu.context.expected_student_failed, :title => "Student Fails"

Now with the data parameters available in my view, I call the
divide_numbers method with the values of those parameters so if
expected_student_failed was an empty value in database, that empty value
gets passed as the second argument:

= render "dashboard/progressbar.html", :value =>
divide_numbers(actual.to_f, expected), :text => "#{actual} /
#{expected}"

Then the method is executed in format_helper:

def divide_numbers(x, y)
  result = x / y
  result.to_s == ''NaN'' ? 0 : result
rescue 0
end

If y is nothing (empty), the error occurs. If y is an integer the error
doesn''t occur. Doesn''t this line take all non numbers like
empty and
convert it to integer 0:
result.to_s == ''NaN'' ? 0 : result

If that''s the case, then why do I get the error?

Will I be forced to do this (i haven''t tested this yet but I presume it
would work):

def divide_numbers(x, y)
  result = x / y
  if result.nil?
   result.to_s = 0
  else
   result.to_s == ''NaN'' ? 0 : result
  end
rescue 0
end


Thanks for response.

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On Mon, Mar 28, 2011 at 4:02 PM, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Hey all,
>
> I get the following error message:
> ActionView::TemplateError (class or module required for rescue clause)
> in app/vie$ app/helpers/format_helper.rb:116:in `divide_numbers''
>
>
> Basically I have a field in database called Student Fails and I populate
> fields with data. Sometimes the value can be empty - not null, not
> integer, just empty because when user updates record they clear out
> field and update it. First in my progressbar file I render a partial
> called progressbar_item, passing in the string to the partial in render
> method as well as data parameters that I can use in my progressbar file:
>
>
>      = render "dashboard/progressbar_item.html", :actual =>
> @student_counters[:student_failed], :expected =>
> cu.context.expected_student_failed, :title => "Student Fails"
>
> Now with the data parameters available in my view, I call the
> divide_numbers method with the values of those parameters so if
> expected_student_failed was an empty value in database, that empty value
> gets passed as the second argument:
>
> = render "dashboard/progressbar.html", :value =>
> divide_numbers(actual.to_f, expected), :text => "#{actual} /
> #{expected}"
>
> Then the method is executed in format_helper:
>
> def divide_numbers(x, y)
>  result = x / y
>
This line will raise an error if y is nil or blank... It won''t even get
to
the next line.

>  result.to_s == ''NaN'' ? 0 : result
> rescue 0
> end
>
> If y is nothing (empty), the error occurs. If y is an integer the error
> doesn''t occur. Doesn''t this line take all non numbers
like empty and
> convert it to integer 0:
> result.to_s == ''NaN'' ? 0 : result
>
> If that''s the case, then why do I get the error?
>
> Will I be forced to do this (i haven''t tested this yet but I
presume it
> would work):
>
> def divide_numbers(x, y)
>  result = x / y
>  if result.nil?
>   result.to_s = 0
>  else
>   result.to_s == ''NaN'' ? 0 : result
>  end
> rescue 0
> end
>
>
> Thanks for response.
>
> --
> Posted via http://www.ruby-forum.com/.
>
> --
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> "Ruby on Rails: Talk" group.
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>
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>
>
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On Mar 28, 10:02 pm, John Merlino
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Hey all,
>
> I get the following error message:
> ActionView::TemplateError (class or module required for rescue clause)
> in app/vie$ app/helpers/format_helper.rb:116:in `divide_numbers''
>
> Basically I have a field in database called Student Fails and I populate
> fields with data. Sometimes the value can be empty - not null, not
> integer, just empty because when user updates record they clear out
> field and update it. First in my progressbar file I render a partial
> called progressbar_item, passing in the string to the partial in render
> method as well as data parameters that I can use in my progressbar file:
>
>       = render "dashboard/progressbar_item.html", :actual =>
> @student_counters[:student_failed], :expected =>
> cu.context.expected_student_failed, :title => "Student Fails"
>
> Now with the data parameters available in my view, I call the
> divide_numbers method with the values of those parameters so if
> expected_student_failed was an empty value in database, that empty value
> gets passed as the second argument:
>
> = render "dashboard/progressbar.html", :value =>
> divide_numbers(actual.to_f, expected), :text => "#{actual} /
> #{expected}"
>
> Then the method is executed in format_helper:
>
> def divide_numbers(x, y)
>   result = x / y
>   result.to_s == ''NaN'' ? 0 : result
> rescue 0
> end
That''s not legal ruby - where you''ve stuck a 0 it''s
expecting a class
name (which sort of exceptions the rescue clause should handle).
You may be mixing things up with the one liner do_foo rescue 0. Also
floats have a nan? method which would be a little nicer than that
string comparison you have there
>
> If y is nothing (empty), the error occurs. If y is an integer the error
> doesn''t occur. Doesn''t this line take all non numbers
like empty and
> convert it to integer 0:
> result.to_s == ''NaN'' ? 0 : result
Not quite. That will only coerce NaN to 0, but it wouldn''t do anything
to Infinity, and of course you wouldn''t even get to this line if y was
something such that x / y was meaningless (ie y is not coercible to a
numeric value). NaN isn''t a placeholder for anything that
isn''t a
number but for specific situations where it isn''t possible to come up
with a more meaningful answer (eg 0.0/0 )

Fred
>
> If that''s the case, then why do I get the error?
>
> Will I be forced to do this (i haven''t tested this yet but I
presume it
> would work):
>
> def divide_numbers(x, y)
>   result = x / y
>   if result.nil?
>    result.to_s = 0
>   else
>    result.to_s == ''NaN'' ? 0 : result
>   end
> rescue 0
> end
>
> Thanks for response.
>
> --
> Posted viahttp://www.ruby-forum.com/.
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On 28 March 2011 22:02, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> If y is nothing (empty), the error occurs. If y is an integer the error
> doesn''t occur.
yup. "divide by zero" will do that...
> Doesn''t this line take all non numbers like empty and
> convert it to integer 0:
> result.to_s == ''NaN'' ? 0 : result
> If that''s the case, then why do I get the error?
Unfortunately, your code is breaking before there, and I doubt it
would work as you expect even if it did (I don''t think you can be sure
the integer would be ''NaN'')

Try this instead:

  def divide_numbers(x, y)
    (x / y) rescue 0
  end

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Thanks for all the responses. My understanding it''s breaking when I try
to pass nothing as an argument to that function because you can''t pass 
an undefined variable as an argument.

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On 30 March 2011 16:45, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Thanks for all the responses. My understanding it''s breaking when
I try
> to pass nothing as an argument to that function because you can''t
pass
> an undefined variable as an argument.
What''s the error message you get? "divide by zero"? or
"1 parameter for 2"?

You earlier said:
> Sometimes the value can be empty - not null, not
> integer, just empty because when user updates record they clear out
> field and update it.
>
> = render "dashboard/progressbar.html", :value =>
divide_numbers(actual.to_f, expected), :

In this event, you *are* passing two parameters to the method, one as
a float (which, if it started as an empty string, will be turned to
0.0) and the expected value, which may be nil (or an empty string), or
a number. Is there anywhere you are ensuring it''s a float like you do
the "actual" value?
Maybe try:
  divide_numbers(actual.to_f, expected.to_f)
...to get more consistent results from a range of input values.

BTW, have a play in the console too, to see what different
combinations give you:

  >> 2/0
  ZeroDivisionError: divided by 0
  >> 2/""
  TypeError: String can''t be coerced into Fixnum
  >> 2/nil
  TypeError: nil can''t be coerced into Fixnum
  >> 2/0.0
  => Infinity
  >>

...try that with your divide_numbers method...

HTH

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