From: Brian Candler <b.candler@...>
Date: 2009-01-16T06:06:57+09:00
Subject: Re: undefined method `[]' for nil:NilClass - how to prevent?

Mmcolli00 Mom wrote:
> I'll am looking to see if maybe I am missing a gem, not sure.
> 
>>Value does not contain a match: Clashifting.rb:55: undefined method `+' for >nil:NilClass (NoMethodError)
..

>     counts[word][i] += 1 #line 55

Well, this expression is a shortcut for

  counts[word][i] = counts[word][i] + 1

so this means that counts[word][i] (on the right hand side) is nil. This 
will occur if a line of your data file has more than 2 columns.

Note that

counts['someword'] is initialised to Array(2,0), which is [0,0]

so:

counts['someword'][0] is 0
counts['someword'][1] is 0
counts['someword'][2] is nil  .. same for [3], [4] etc.

So it's reading past the end of the array, getting nil, and trying to 
add 1 to it. The expression nil + 1 is meaningless, of course.

The solution depends on what you want to happen when your program reads 
a line of the form "a,b,c"

* Do you want to treat "a" as the first word, and "b,c" as the second?
* Do you want to treat "a" and "b" as words, and ignore the rest of the 
line?

Suitable adjustment to the 'split' expression should do the trick.

irb(main):001:0> "a,b,c".split(",",2)
=> ["a", "b,c"]
irb(main):002:0> "a,b,c".split(",")[0,2]
=> ["a", "b"]

HTH,

Brian.
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