From: Craig Demyanovich <cdemyanovich@...>
Date: 2007-07-12T06:27:00+09:00
Subject: Re: Returning part of a hash

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On 7/11/07, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
>
>
> On Jul 11, 2007, at 1:30 PM, barjunk wrote:
>
> > I have hash that has about 20 keys.  I'd like to create a new variable
> > with just three of those keys.  Example:
> >
> > hash = { "key1" => "value1",
> >                "key2" => "value2",
> >                ...
> >                "key20" => "value20" }
> >
> > And a function like:
> > newhash = hash.slice("key2","key5","key7")
> >
> > Which creates:
> >
> > newhash = { "key2" => "value1",
> >                "key5" => "value5",
> >                "key7" => "value7" }
> >
> > hash.select {|key, value| key == "key1" }
> >
> > I could do the above multiple times, but this returns an array not the
> > hash pair.
> >
> > Thanks for any help.
> >
> > Mike B.
>
>
> Hey Mike-
>
>         Here are two handy methods for doing what you want:
>
> class Hash
>    # lets through the keys in the argument
>    # >> {:one => 1, :two => 2, :three => 3}.pass(:one)
>    # => {:one=>1}
>    def pass(*keys)
>      self.reject { |k,v| ! keys.include?(k) }
>    end
>
>    # blocks the keys in the arguments
>    # >> {:one => 1, :two => 2, :three => 3}.block(:one)
>    # => {:two=>2, :three=>3}
>    def block(*keys)
>      self.reject { |k,v| keys.include?(k) }
>    end
>
> end


Ezra,

Since you're adding the #pass and #block methods to Hash and Hash already
has a #keys method, is there a conflict between the *keys parameter to #pass
and #block and the #keys method on Hash?

Thanks,
Craig

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