From: Phrogz <phrogz@...>
Date: 2007-12-11T23:45:47+09:00
Subject: Re: Find the first non-nil element in an array

On Dec 11, 2:28 am, Stefano Crocco <stefano.cro...@alice.it> wrote:
> Alle marted́ 11 dicembre 2007, lianliming ha scritto:
>
>
>
> > Hi all,
>
> > Is there any build-in method of class Array which can be used to find
> > the first non-nil element in an array? I can't find any so I am trying
> > to achieve it by my own approach. I don't think my approach is smart
> > enough, so I would like to know better one to do so. Here is what I am
> > doing:
>
> > a = [nil, "hello", "world"]
> > b = a
> > b.compact!
> > first_non_nil_elem =  b.first
>
> > I don't call "compact!" directly on a because it will change a's
> > structure, I want to reserve nil elements in a.
>
> > Any suggestions are really appreciated!
>
> You can use Enumerable#find, which will return the first item in the array for
> which the block returns true:
>
> a = [nil, "hello", "world"]
> puts a.find{|i| !i.nil?}
> => "hello"
>
> By the way, you can use compact, instead of compact! to avoid using the
> temporary variable b:
>
> a = [nil, "hello", "world"]
> first_non_nil_elem = a.compact.first
>
> While compact! removes the nil elements from the receiver, compact returns a
> new array with the nil element removed.

Moreover, there was no reason to assign to the 'b' variable in the
first place. Doing so doesn't duplicate the array, but just creates
another reference to it. The compact! method still modified the same
array:

  irb(main):006:0> a = [ nil, "foo", "bar" ]
  => [nil, "foo", "bar"]

  irb(main):007:0> b = a
  => [nil, "foo", "bar"]

  irb(main):008:0> b.compact!
  => ["foo", "bar"]

  irb(main):009:0> a
  => ["foo", "bar"]

So if the intent was, as I assume, to preserve the original array with
the nil values, that's even more reason to use #compact instead of
#compact!