From: "David A. Black" <dblack@...>
Date: 2009-08-28T19:43:26+09:00
Subject: Re: data sctructure

--1926193751-335579791-1251456191=:18012
Content-Type: MULTIPART/MIXED; BOUNDARY="1926193751-335579791-1251456191=:18012"

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

--1926193751-335579791-1251456191=:18012
Content-Type: TEXT/PLAIN; charset=EUC-KR; format=flowed
Content-Transfer-Encoding: 8BIT

Hi --

On Fri, 28 Aug 2009, Juliano 層硲 wrote:

> Hello guys.
>
> I've just started using ruby and I come from Python... I'm still
> learning to think the Ruby way...
> Of course, any beginning is hard, but even so I've been having a lot
> of fun learning Ruby.

Welcome! I'm glad you're enjoying it.

> The problem is that I still don't know much about the tons of methods
> and I'm maybe letting something pass through my fingers.
>
> My problem is this:
> I have to read a file and set up a data structure of embedded
> dictionaries. In Python I can easily do that by means of
> "dict.defaultdict()", but I didn't understand how to do that in
> Ruby... I finally came up with the following:
>
>  def preprocess(lines)
>    d = {}
>    lines.each do |line|
>      c, s, fc, fl = line.split("\t")
>        if !d.has_key? c
>          d[c] = {}
>        end
>        if !d[c].has_key? s
>          d[c][s] = {}
>        end
>        if !d[c][s].has_key? fc
>          d[c][s][fc] = []
>        end
>      d[c][s][fc].push fl
>    end
>    return d
>  end
>
> My question is: Is there an easier way to do this in Ruby as it is in
> Python?

The idiom for conditional assignment in Ruby is ||= (or-equals). You
could do this:

   def preprocess(lines)
     d = {}
     lines.each do |line|
       c, s, fc, fl = line.split("\t")
       d[c]        ||= {}
       d[c][s]     ||= {}
       d[c][s][fc] ||= []
       d[c][s][fc].push fl
     end
     return d
   end

The only thing is, in cases where you want false or nil to be a hash
value, ||= will over-eagerly do the assignment. But that's not the
case here.

There are also ways to set the default behavior of hashes, but I think
the above is probably the most direct way to do what you want.


David

-- 
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com

September Ruby training in NJ has been POSTPONED. Stay tuned 
for updates!
--1926193751-335579791-1251456191=:18012--
--1926193751-335579791-1251456191=:18012--