From: John Carter <john.carter@...>
Date: 2008-01-23T11:36:46+09:00
Subject: Re: How to improve this code?

On Wed, 23 Jan 2008, Jair Rillo Junior wrote:

> Hi guys,
> I am new in the Ruby world, I am coming from Java, and I would like to
> "think " in Ruby instead Java.
>
> I did a code to read a CSV file (separated by comma), organize the
> values and print the output.

Probably the mostly useful first thought in Ruby is... "Nah, I bet
it's in the standard library somewhere, better check ruby-doc.org"

From standard library module 'csv'

   # Open a CSV formatted file for reading or writing.
   #
   # For reading.
   #
   # EXAMPLE 1
   #   CSV.open('csvfile.csv', 'r') do |row|
   #     p row
   #   end
   #
   # EXAMPLE 2
   #   reader = CSV.open('csvfile.csv', 'r')
   #   row1 = reader.shift
   #   row2 = reader.shift
   #   if row2.empty?
   #     p 'row2 not find.'
   #   end
   #   reader.close
   #
   # ARGS
   #   filename: filename to parse.
   #   col_sep: Column separator.  ?, by default.  If you want to separate
   #     fields with semicolon, give ?; here.
   #   row_sep: Row separator.  nil by default.  nil means "\r\n or \n".  If you
   #     want to separate records with \r, give ?\r here.
   #
   # RETURNS
   #   reader instance.  To get parse result, see CSV::Reader#each.
   #
   #
   # For writing.
   #
   # EXAMPLE 1
   #   CSV.open('csvfile.csv', 'w') do |writer|
   #     writer << ['r1c1', 'r1c2']
   #     writer << ['r2c1', 'r2c2']
   #     writer << [nil, nil]
   #   end
   #
   # EXAMPLE 2
   #   writer = CSV.open('csvfile.csv', 'w')
   #   writer << ['r1c1', 'r1c2'] << ['r2c1', 'r2c2'] << [nil, nil]
   #   writer.close
   #
   # ARGS
   #   filename: filename to generate.
   #   col_sep: Column separator.  ?, by default.  If you want to separate
   #     fields with semicolon, give ?; here.
   #   row_sep: Row separator.  nil by default.  nil means "\r\n or \n".  If you
   #     want to separate records with \r, give ?\r here.
   #
   # RETURNS
   #   writer instance.  See CSV::Writer#<< and CSV::Writer#add_row to know how
   #   to generate CSV string.
   #


> My initial thought was store the values into a Hash object, where the
> KEY is the email (column a) and the value is an Array containing the
> values (column b).
> Going through all lines, test if the email address already exists in the
> Hash, if so update the Array, otherwise create a new entry into the
> Hash.

My flavourite idiom is...
   require 'set'
   h = Hash.new{|hash,key| hash[key] = Set.new}

then in the loop..
   values = lines.split(",")
   email = values.shift
   h[email].merge(values)

Ooh... That's just sooo pretty!




John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
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