From: gotoken@... (GOTO Kentaro)
Date: 2001-03-06T23:25:13+09:00
Subject: [ruby-talk:12136] Re: Weird Array behavior

In message "[ruby-talk:12130] Weird Array behavior"
    on 01/03/06, jjthrash@pobox.com <jjthrash@pobox.com> writes:
>array = [[12345, "val"],[23456, "val2"],[34567, "val3"],[45678,"val4"]]
>oldArray = array
>array = Array.new((oldArray.size.to_f/3).ceil, Array.new(2))
>oldArray.each_with_index do |entry, index|
>   if array[(index.to_f/3).floor][0] == nil
>      array[(index.to_f/3).floor][0] = entry[0]
>      #INSPECTION POINT

>If I debug and step up to the first time I reach the INSPECTION
>POINT, I expect the value array to be
>[[12345, nil], [nil, nil]], but it's actually
>[[12345, nil], [12345, nil]]

Array.new fills always with an *identical* object, specified as the
2nd argument.  So we have to fill *after* create an array. 

Each of the following create empty an array consists of empty arrays:

  #1 straightforward
  array = []
  (oldArray.size.to_f/3).ceil.times{ array.push Array.new(2) }

  #2 intuitive
  array = Array.new((oldArray.size.to_f/3).ceil).map{Array.new(2)}

  #3 faster than the above
  (array = Array.new((oldArray.size.to_f/3).ceil)).map!{Array.new(2)}

-- Gotoken