Hi --

On Thu, 2 Jul 2009, Bil Kleb wrote:

>  Hi,
> 
>  Given an array of integers, I need to delete all those
>  entries that are lower than the current array index.
> 
>  I first thought of the non-existent,
> 
>  array.delete_if_with_index{ |e,i| e < i }
> 
>  then,
> 
>  remove_indices = []
>  array.each_with_index{ |e,i| remove_indices << i if e < i }
>  array.delete_at( remove_indices )
> 
>  or the same, but with a fictious inject_with_index,
> 
>  remove_indices = inject_with_index([]){|acc,e,i| acc << i if e < i }
>  array.delete_at( remove_indices )
> 
>  and finally the 1.9 possibility,
> 
>  array.map_with_index!{ |e,i| e < i ? nil : e }.compact!
> 
>  before compromising with
> 
>  array = (0...array.size).zip(array).map{ |i,e| e < i ? nil : e }.compact
> 
>  Anything more elegant available?
> 
>  Or perhaps an alternative way to attack the problem?

In 1.9 I would do:

> > a = [0,1,2,1,4,3,6,7,2]
=>  [0, 1, 2, 1, 4, 3, 6, 7, 2]
> > a.reject!.with_index {|e,i| e < i }
=>  [0, 1, 2, 4, 6, 7]

In 1.8 I'm not coming up with anything more elegant than:

> > a.values_at(*(0...a.size).reject {|i| a[i] < i })
=>  [0, 1, 2, 4, 6, 7]

or some variant thereof.


David

-- 
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Now available: The Well-Grounded Rubyist (http://manning.com/black2)
"Ruby 1.9: What You Need To Know" Envycasts with David A. Black
http://www.envycasts.com