From: Brian Candler <b.candler@...>
Date: 2008-12-10T06:55:10+09:00
Subject: Re: compare 2 text files - check for difference - Please help

Mmcolli00 Mom wrote:
> require 'diff/lcs/Array'
> 
> file = File.open("1.txt",'r')
>  @row = {}
>     file.each_line do |@line|
>       key, val = @line.chomp.split(",",0)
>       @row[key] = val
>   end
> 
>  file2 = File.open("2.txt",'r')
>  @row2 = {}
>     file2.each_line do |@line2|
>       key2, val2 = @line2.chomp.split(",",0)
>       @row2[key2] = val2
>   end
> 
> 
> puts diffs = Diff::LCS.diff(@line,@line2)

You are using a very odd way of iterating, which is explicitly forbidden 
in ruby 1.9. If you write

  foo.each do |@bar| ...

then for each element of foo, the instance variable @bar is set to that 
element. So the net result here is that after the loops have finished, 
@line remains set to the last line of 1.txt, and @line2 remains set to 
the last line of 2.txt. You can demonstrate this by adding

  p @line, @line2

just before calling Diff::LCS.

(In ruby 1.9, block parameters must be local variables, and are always 
local to the block - they always drop out of scope afterwards)

So, your test program simplifies to the following:

require 'rubygems'
require 'diff/lcs/array'

@line = "1,2\n"
@line2 = "1,2,3\n"
puts diffs = Diff::LCS.diff(@line,@line2)

The question is, what do you expect this to do?

If you replace 'puts' with 'p' in the last line, you get the following 
more detailled output:

[[#<Diff::LCS::Change:0xb7be613c @element=",", @action="+", 
@position=3>, #<Diff::LCS::Change:0xb7be60d8 @element="3", @action="+", 
@position=4>], [#<Diff::LCS::Change:0xb7be5fac @element="", @action="-", 
@position=4>]]

My guess is that Diff::LCS is treating the string as a sequence of 
bytes. The first change is [add "," at pos 3, add "3" at pos 4], which 
is correct. The second change is strange, as it seems to say ["remove 
nothing from pos 4"]

However, since all the examples in the README show two arrays being 
passed, and here you're passing in two strings, I'm not sure this is 
even a supported way of working with this library.

Your code also builds two hashes, @row and @row2, but doesn't seem to 
use them at all. Were you trying to do something with them?

Finally, your use of split may not behave the way you expect:

irb(main):002:0> key2, val2 = "1,2,3\n".chomp.split(",",0)
=> ["1", "2", "3"]
irb(main):003:0> key2
=> "1"
irb(main):004:0> val2
=> "2"

That is, you're ignoring everything after the second field.

I can strongly recommend playing around with expressions in irb, and 
adding snippets of "p ..expression.." within your code, to get a feel 
for what's happening.

HTH,

Brian.
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