Re: [ ruby-Patches-9055 ] Dynamic Array#join with block

On Mar 6, 2007, at 7:00 AM, Farrel Lifson wrote:

> This example can use inject  (see bleow)  however inject does not
> handle the recursive 'flattening' functionality that the current
> implementation of join has when it encounters nested arrays in the
> general case. For instance
> [[1,2],[3,4]].join(',')
> produces
> "1,2,3,4"
> and the patch handles things the same way
> [[1,3],[2,4]].join{|sep,a,b| a > b ? ">" : "<"}
> will produce
> "1<3>2<4"
>
> If you tried to use inject to do this it would probably get hairy. I
> implemented the example given using inject and it doesn't look that
> pretty:
> ary = [1,3,2,4];idx=1
> result = ary.inject("") do |memo,num|		
> 	memo += "#{num}" + (idx < ary.length ? " which is" + ((num >
> ary[idx]) ? " #{num - ary[idx]} more" : " #{ary[idx] - num} less") + "
> than " : "")
> 	idx+=1			
> 	memo
> end	
>
> Trying to deal with possible recursive flattening cases would probably
> make it look worse.

Hmm, it's not that difficult, but it is definitely more work than join:

   ary = [1,3,2,4]  # or [[1,3],[2,4]].flatten
   ary[2..-4].inject(a[0..0]) { |a,e| a << (a[-1] > e ? ">" : "<"); a  
<< e }.join


Jim