From: Srijayanth Sridhar <srijayanth@...>
Date: 2008-07-01T21:54:36+09:00
Subject: Re: Hash#select returns an array but Hash#reject returns a hash...

Well put. Thanks again.

Jayanth

On Tue, Jul 1, 2008 at 6:18 PM, David A. Black <dblack@rubypal.com> wrote:
> Hi --
>
> On Tue, 1 Jul 2008, Srijayanth Sridhar wrote:
>
>>>
>>> that will change in newer version of ruby, eg ruby1.9
>>>
>>> irb(main):015:0> RUBY_VERSION
>>> => "1.9.0"
>>> irb(main):016:0> a=Hash.new
>>> => {}
>>> irb(main):017:0> a[1]=2
>>> => 2
>>> irb(main):018:0> a[2]=2
>>> => 2
>>> irb(main):019:0> a[3]=4
>>> => 4
>>> irb(main):020:0> a.select { |key,value| value > 2 }
>>> => {3=>4}
>>> irb(main):021:0> a.reject { |key,value| value <= 2 }
>>> => {3=>4}
>>>
>>> kind regards -botp
>>>
>>>
>>
>> Thanks.
>>
>> So this is just some sort of artefact/legacy code that never got changed?
>
> You can actually make a case that select and reject are not exactly
> symmetrical operations. Imagine a line of people:
>
>
>    Joe John Joan David Jim Jenny Jeff Matz
>
> If I tell everyone in the line whose name does not begin with J to
> step backwards (reject), the original line is smaller but it's still
> the same line.
>
> If I tell everyone whose name *does* begin with J to step forwards
> (select), I've got a new line of J people.
>
> "Same line" and "new line" don't necessarily map to "same object" and
> "new object" in Ruby (since the post-reject hash is a different hash).
> But it suggests that there's a difference, arguably, between select
> and reject, in terms of the formal disturbance of the object, which in
> turn makes it easier to understand why select would return objects in
> a different container, while reject would leave the container in the
> same form but just contain fewer things.
>
> However, that doesn't mean it's bad for select to return a hash (which
> it does, as was mentioned, as of 1.9). Just that the behavior of one
> doesn't necessarily imply the behavior of the other.
>
>
> David
>
> --
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>
>