From: Rick DeNatale <rick.denatale@...>
Date: 2009-09-27T00:23:38+09:00
Subject: Re: How to remove duplicate elements in a 2D array

On Sat, Sep 26, 2009 at 10:56 AM, Li Chen <chen_li3@yahoo.com> wrote:
> Thairuby ->a, b {a + b} wrote:
>> The method ".map(&:flatten)" is use to converse hash back to array.
>
>
> Thanks.
>
> But I still have some doubts about this line:
>
>  result = arr.inject({}){|x,y| x[y[0]]=y[1..-1];
>               x
>              }.map(&:flatten)
>
>
> 1) When I look at #inject method, I notice it only takes either no
> augument or
> an augument with initial value. But in your code it takes a hash. It is
> kind of new/strange to me.

It's giving it an empty hash as the initial value, nothing strange at all.


> 2) Why do you  write an x alone after this line  x[y[0]]=y[1..-1]; ?

So that the result of the block is the hash and not y[1..-1] which is
the value of the assignment.
>
> 3) #map(&:flatten) doesn't work in my Ruby version(1.8.6). Which version
> are you using? But I make some changes and it works.
>
> result = arr.inject( {  }  ){|x,y| x[y[0]]=y[1..-1]; x}.to_a
> r=result.collect { |row| row.flatten}

I'm guessing that he's using either 1.8.7 or 1.9  both of which define
Symbol#to_proc which allows this, or perhaps he's using the
activesupport gem which is part of Rails and defines this as well.


I like David Black's alternative suggestion:

  result = arr.inject({}){|x,y| x[y[0]]=y; x}.values

Note that neither of these preserve the ordering of the rows retained
from the original array in Ruby 1.8.x, but if you're happy I guess
that's not a requirement.

-- 
Rick DeNatale

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