why does my method return an error if argument is not a number?

rubyonrails-talk
1

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.

2

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.

3

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

4

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

5

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.

6

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