From: Morton Goldberg <m_goldberg@...>
Date: 2007-04-09T16:50:02+09:00
Subject: Re: Nesting Array loops

On Apr 9, 2007, at 2:49 AM, Rubic wrote:

> I new to Ruby and I have lost touch with whatever little programming I
> did know a few years back. Sorry if this is a lame question.
>
> How does one nest arrays?
>
> I want to check every element of the array and compare it against rest
> of the elements of that array for repeat occurences. but for now I did
> be happy if I can get to even print the 2 values, hence 'puts #i,  
> #j' in
> the code.
>
>
>   f = File.open("iplist.txt")
>   f1 = File.open("iplist.txt")
>   f.each  { |i|
>     f1.each { |j|
>      puts "#{i}, #{j}"
>    }
> }
>
> With the above code I only get output of one successful iteration of
> f.each and it stops and doesnt continue for the rest of the values of
> f.each.

The problem is that both f and f1 are pointing to the same disk file.  
After the first iteration using f, the disk file is at EOF. When f1  
attempts to iterate further, it sees the EOF and terminates.

If you read the whole file into an array, your approach will work:

<code>
f = File.read("/Users/mg/Desktop/test.txt")
f = f.map { |e| e.chomp } # get rid on newlines
puts f
puts
f.each do |i|
    f.each { |j| puts "#{i}, #{j}" }
end
</code>

<result>
quick
fox
brown
fox

quick, quick
quick, fox
quick, brown
quick, fox
fox, quick
fox, fox
fox, brown
fox, fox
brown, quick
brown, fox
brown, brown
brown, fox
fox, quick
fox, fox
fox, brown
fox, fox
</result>

However, to go back to your original problem of detecting duplicates,  
there are better ways. Here is one:

<code>
# Array#uniq removes duplicates.

def has_dups?(ary)
    ary.size != ary.uniq.size
end

f = File.read("/Users/mg/Desktop/test.txt")
f = f.map { |e| e.chomp } # get rid on newlines
has_dups?(f) # => true
has_dups?(f.uniq) # => false
</code>

Regards, Morton