From: Robert Klemme <shortcutter@...>
Date: 2009-01-15T16:04:12+09:00
Subject: Re: undefined method `[]' for nil:NilClass - how to prevent?

On 15.01.2009 05:51, Mmcolli00 Mom wrote:
> This returns correct value so long as I do not use array[0][i]. The
> error is:
> 
>> searchArray.rb:13: undefined method `[]' for nil:NilClass (NoMethodError)
>>  from shifting1.rb:7:in `each_line'
>>  from shifting1.rb:7
>> Exit code: 1
>>
> #**************************************
> #Searches through a text file and, at one row at a time, counts how many
> occurrences of the value exist for the column. For instance, if word,
> 'bird' exists in column1 row1 then count how many birds exist for the
> whole column. Next..count the occurrences of bird in the column 2. If
> the numbers do not match then outputs "Value does not contain a match:"
> +Value.
> 
> I am having this issue with NilClass a lot this week. What do you think
> I should change?

The whole piece of code.  No seriously, there are quite a few things to say:


> ##start code
> 
>  col1 = 0
>  col2 = 0
> 
>  File.open('temp.txt', 'r+').each_line do |temp|

The file handle is not closed properly.  Rather use the block form of 
File.open.  Also, since you do not write the file, you can as well use

File.foreach 'temp.txt' do |temp|
...
end

Btw, the name "temp" doesn't tell much about the contents of the 
variable.  I'd pick another, more meaningful name like "line".

>    array = []

Superfluous initialization...

>    i = 0
>   array = temp.chomp.split(",",0)

... because here you overwrite "array" immediately without reading it.

>    arrayVal1 = array[0][i]
>    arrayVal2 = array[1][i]
> 
>      if array[0] == arrayVal1 then

As far as I can see this does not make sense: the comparison can never 
be "true" because you compare an object (array[0]) with part of it 
(array[0][i]).

>        col1 = col1 + 1
>       end
> 
>      if array[1] == arrayVal2 then
>        col2 = col2 + 1
>     end
>      i = i + 1
> 
>   if col1 != col2 then
>     puts "Value does not contain a match:"
>     puts arrayVal1
>  end

I have no idea what this is supposed to do: you compare global counts of 
matches for every line.  But: if there once was a mismatch in a line, 
counts will not be the same in the next matching line.  Is this really 
what you want?  Your description does not make this clear.

> end
> 
> ##end code
> 
> Attachments:
> http://www.ruby-forum.com/attachment/3164/searchArray.rb

The whole bit certainly does not match your description.  How about:

counts = values = nil

File.foreach 'temp.txt' do |line|
   line.chomp!
   # better use CSV parsing:
   fields = line.split ','

   if values
     fields.each_with_index |f,i|
       counts[i] += 1 if values[i] == f
     end
   else
     # init search strings
     values = fields
     counts = Array.new(values.size, 0)
   end
end

Cheers

	robert

-- 
remember.guy do |as, often| as.you_can - without end