From: "David A. Black" <dblack@...>
Date: 2009-07-02T21:55:10+09:00
Subject: Re: delete_if_with_index or delete_at(array) in 1.8.6?

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

-- 
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