From: William James <w_a_x_man@...>
Date: 2005-09-06T17:46:31+09:00
Subject: Re: how to do insertion and smooth traversal simultaneously on array

SHIGETOMI, Takuhiko wrote:
> greetings, guys.
>
> this is a pseudo-ruby code which shows what i am expecting.
>
> a = [ 0, 1, 2, 3, 4, 5 ]
> a.each_with_index do |x, i|
>   puts "[#{i}] : #{x}"
>   if i % 2 == 0  # even index ?
>     a.insert( i, ':-)' )
>     skip 1 # <- this is a pseudo directive to skip the next element
>            #    which has just been inserted now
>   end
> end
> puts a.size
>
> expected output...
>
> [0] : 0
> [1] : 1
> [2] : 2
> [3] : 3
> [4] : 4
> [5] : 5
> 9         <-- means that 3 smileys have been inserted
>
> as above, i want to traverse an array with some conditional insertion to
> itself.

If the array is "flat":
-----------------------------------------
a = [ 0, 1, 2, 3, 4, 5 ]
a.each_with_index do |x, i|
  if i % 2 == 0  # even index ?
    a[i] = [ ":-)", x ]
  end
end
a.flatten!
p a
-----------------------------------------
[":-)", 0, 1, ":-)", 2, 3, ":-)", 4, 5]


If the array isn't flat:
-----------------------------------------
a = [ [81,"&"], 82, 83, [84,"@"], 85 ]
a = (0...a.size).to_a.zip(a)
p a
a = a.inject([]) { |ary,x|
  if x[0] % 2 == 0  # even index ?
    ary += [ ":-)", x[1] ]
  else
    ary << x[1]
  end
}
p a
-----------------------------------------
[[0, [81, "&"]], [1, 82], [2, 83], [3, [84, "@"]], [4, 85]]
[":-)", [81, "&"], 82, ":-)", 83, [84, "@"], ":-)", 85]