From: Austin Ziegler <austin@...>
Date: 2003-03-29T03:45:45+09:00
Subject: Re: Array question

On Fri, 28 Mar 2003 22:48:19 +0900, walter@mwsewall.com wrote:
>>> |#I want to do this
>>> |puts list.join(","){|item| item.downcase}
>>> |
>>> |#but I have to do this
>>> |puts list.collect{|item| item.downcase}.join(",")

> I didn't actually want to change the array items themselves, just
> use the results of the block for the join. If there was no block
> it would work just as it does now joining the array element
> directly.

> I have only used Ruby for a couple of weeks and I have used this
> type of thing at least a few times. collect then join works, I
> just thought it would be faster and use less memory if join took a
> block and did it directly.

> It would also seem similar to me to the way that sort works.
> Without a block sort uses <=> but if given a block it will use the
> results of that for the sorting. I was looking for the same basic
> functionality for join.

Your example could be done, however, with:

puts list.join(", ").downcase

If you wanted to use #capitalize, though, you need to collect.

I think that join could take a block, but I'd want it to be more
like:

  list.join do |current, next|
    if next.nil?
      ""
    elsif (next - current) > 1
      " ... "
    else
      ", "
    end
  end

Thus, if my list is:

  list = [1, 2, 3, 5, 8, 9, 10]

the result would be:

  1, 2, 3 ... 5 ... 8, 9, 10

-austin (sample code follows)

class Array
  def blockjoin
    val = ""
    each_with_index do |e, i|
      sep = yield e, self[i + 1]
      val << e.to_s << sep
    end
    val
  end
end

list = [1, 2, 3, 5, 8, 9, 10]

puts list.blockjoin { |c, n|
  if n.nil?
    ""
  elsif (n - c) > 1
    " ... "
  else
    ", "
  end
}

-- Austin Ziegler, austin@halostatue.ca on 2003.03.28 at 13:29:09