From: ts <decoux@...>
Date: 2003-05-01T00:46:13+09:00
Subject: Re: Arrays

>>>>> "O" == Orion Hunter <orion2480@hotmail.com> writes:

irb> a = Array.new( 4, Array.new )

 Well, with 1.8 you'll able to write

pigeon% ruby -e 'a = Array.new(4) { [] }; a[0][0] = 1; p a'
[[1], [], [], []]
pigeon% 


O> My next approach was to create the array, with a dafault length, and iterate 
O> over it assigning a new array to each element:

 there is a problem : you assign a new array to the variable `i' and not to
 each element

O>     my_arr = Array.new( 4 )
O>     my_arr.each{ |i|

 at this step the variable `i' reference an element of the array

O>         i = Array.new

 but here  `i' will make reference to a new Array

O>     }

 This is like if you write :

    i = my_arr[0]
    i = []

 for the first line , `i' make reference to the object `nil' (my_arr[0])
 but in the second line, it will make reference to the object `[]' and
 my_arr[0] is not modified

 but you can write

pigeon% cat b.rb
##!/usr/bin/ruby
my_arr = (1..4).collect { [] }
my_arr.each {|i| i << 1}
p my_arr
pigeon%

pigeon% b.rb
[[1], [1], [1], [1]]
pigeon% 

 `<<' will modify the current element


Guy Decoux