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comp.lang.ruby

"Joining" strings which may be nil (or) Handling Option hashes

Gavri Fernandez

2/13/2005 4:25:00 PM

Hi everyone,
I want to create a query based on options passed in through
an options hash to my method.

The query would look like
"title:ruby and author:dave and publisher:oreilly"
or
"title:ruby and publisher:addison-wesley"
or
"author:dave"
or some other combination based on what options have been set in the hash.

options[:author] |= "" followed by Array#join doesn't help me
because it would lead to successive 'and's in the query.

What is the Ruby Idiom to achieve what I want?

TIA
--
Gavri
---------------------------------------------------
I blog here: http://gavri.bl...
8 Answers

Robert Klemme

2/13/2005 4:43:00 PM

0


"Gavri Fernandez" <gavri.fernandez@gmail.com> schrieb im Newsbeitrag
news:e3ecfac705021308253ae8704e@mail.gmail.com...
> Hi everyone,
> I want to create a query based on options passed in through
> an options hash to my method.
>
> The query would look like
> "title:ruby and author:dave and publisher:oreilly"
> or
> "title:ruby and publisher:addison-wesley"
> or
> "author:dave"
> or some other combination based on what options have been set in the hash.
>
> options[:author] |= "" followed by Array#join doesn't help me
> because it would lead to successive 'and's in the query.
>
> What is the Ruby Idiom to achieve what I want?

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"

Kind regards

robert

Francis Hwang

2/13/2005 5:02:00 PM

0

On Feb 13, 2005, at 11:44 AM, Robert Klemme wrote:
> 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"

Maybe the OP isn't worried about this, but: Is there a way to represent
ORs as well as ANDs if you're doing this?

Francis Hwang
http://f...

Gavri Fernandez

2/13/2005 5:03:00 PM

0

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

Thanks Robert
--
Gavri
---------------------------------------------------
I blog here: http://gavri.bl...

Robert Klemme

2/13/2005 5:34:00 PM

0


"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

Robert Klemme

2/13/2005 5:52:00 PM

0


"Francis Hwang" <sera@fhwang.net> schrieb im Newsbeitrag
news:0682b7cb1757683cfdf7811804277529@fhwang.net...
> On Feb 13, 2005, at 11:44 AM, Robert Klemme wrote:
>> 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"
>
> Maybe the OP isn't worried about this, but: Is there a way to represent
> ORs as well as ANDs if you're doing this?

You could provide multiple values for a key and create an OR from that:

opts = {"title"=>["ruby","foobar"], "author"=>"dave"}

opts.inject(nil) do |s,(k,v)|
if v
(s ? s << " and " : "") <<
(Enumerable === v && ! (String === v) ?
v.inject(nil) {|s2,v2| (s2 ? s2 << " or " : "(") << k << ":" << v2} <<
")" :
"#{k}:#{v}")
else
s
end
end

Slightly unreadable... :-)) You don't need the outer if-else-end though if
v is never nil.

Kind regards

robert

William James

2/13/2005 9:43:00 PM

0

Robert Klemme wrote:
>
> 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"


I prefer this:

opts.to_a.map{|x| x.join('=') if x[1]}.compact.join(' and ')

----> "title=ruby and author=dave and publisher=oreilly"

Gavri Fernandez

2/14/2005 1:07:00 PM

0

On Mon, 14 Feb 2005 02:35:02 +0900, Robert Klemme <bob.news@gmx.net> wrote:

> 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

My bad. My mail was cluttered with
1) The problem
2) Possible solution by handling unused options by not considering them.
3) Possible solution by setting unused options as nil and handling
them while "joining"

Anyway, thanks for the solutions.


--
Gavri
---------------------------------------------------
I blog here: http://gavri.bl...

William James

2/15/2005 1:15:00 AM

0


William James wrote:
> Robert Klemme wrote:
> >
> > 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"
>
>
> I prefer this:
>
> opts.to_a.map{|x| x.join('=') if x[1]}.compact.join(' and ')
>
> ----> "title=ruby and author=dave and publisher=oreilly"

Too prolix. Better:

opts.map{|x| x.join('=') if x[1]}.compact.join(' and ')

Here are the stages through which the data travels:

{"title"=>"ruby", "author"=>"dave", "foo"=>nil, "publisher"=>"oreilly"}
["title=ruby", "author=dave", nil, "publisher=oreilly"]
["title=ruby", "author=dave", "publisher=oreilly"]
"title=ruby and author=dave and publisher=oreilly"