From: Robert Klemme <bob.news@...>
Date: 2005-02-14T02:35:02+09:00
Subject: Re: "Joining" strings which may be nil (or) Handling Option hashes


"Gavri Fernandez" <gavri.fernandez@gmail.com> schrieb im Newsbeitrag 
news:e3ecfac705021309023584319f@mail.gmail.com...
> On Mon, 14 Feb 2005 01:44:57 +0900, Robert Klemme <bob.news@gmx.net> 
> wrote:
>>
>> "Gavri Fernandez" <gavri.fernandez@gmail.com> schrieb im Newsbeitrag
>> news:e3ecfac705021308253ae8704e@mail.gmail.com...
>
>> Lots of, here are some:
>>
>> >> opts = {"title"=>"ruby", "author"=>"dave", "publisher"=>"oreilly",
>> >> "foo"=>nil}
>> => {"title"=>"ruby", "author"=>"dave", "foo"=>nil, 
>> "publisher"=>"oreilly"}
>> >> opts.select{|k,v|v}
>> => [["title", "ruby"], ["author", "dave"], ["publisher", "oreilly"]]
>> >> opts.select{|k,v|v}.map{|k,v| "#{k}=#{v}"}.join(" and ")
>> => "title=ruby and author=dave and publisher=oreilly"
>>
>> Here's a more efficient variant - using #inject of course :-)
>>
>> >> opts.inject(nil){|s,(k,v)| v ? (s ? s << " and " : "") << k << "=" << 
>> >> v :
>> >> s}
>> => "title=ruby and author=dave and publisher=oreilly"
>
>
> This is the solution I hit upon right after I sent my mail. Please
> critique while I try to understand your solutions :)
>
> def get_query(options)
>    query_fragments = []
>    options.each do |key, value|
>        query_fragments.push("#{key.id2name}:#{value}")
>    end
>    query = query_fragments.join(" and ")
> end

I'm missing the condition.  As far as I understood you you want to be able 
to skip nil values.  Did I get this wrong?  Apart from that it does 
certainly what you want.  If you want to spare the intermediate array you 
can do a bit optimization:

def get_query(options)
  q = nil
  options.each do |k,v|
    q = (q ? q << " and " : "") << k << ":" << v
  end
  q
end

This is basically a verbose variant of my inject version.

> Thanks Robert

You're welcome!

Kind regards

    robert