From: Robert Klemme <shortcutter@...>
Date: 2011-05-17T16:14:51+09:00
Subject: Re: Re (2): Linux utility with reverse index facility?

On Mon, May 16, 2011 at 9:40 PM,  <no.top.post@gmail.com> wrote:
> In article <r5g7a8-3a5.ln1@206-248-139-163.dsl.teksavvy.com>, "Chris F.A. Johnson" <cfajohnson@gmail.com> wrote:
>
>> On 2011-05-16, no.top.post@gmail.com wrote:
>> > awk &stuff can "give me the the Nth element",
>> > but, without writing your own search-loop,
>> > what can "give me the index of the 'element'
>> > which is <elementValue>" ?
>> >
>> > I think it's called 'reverse indexing' ?
>>
>>    Do you want 'grep -n'?
>>
>>    If not, please be more specific.
>
> awk & grep are not typically used on arrays of single chars,
> but that's the simplest, to ilustrate the concept.
> Given the 6char array: [abcdef]
> <elementValue> means the value of the element.
> The first element has value "a".
> "the  index of the 'element' which is "e" is
> <the 5th element>; which index is  4 or 5 depending
> on whether you count from 0 or 1 respectively.
>
> So what did I mean by "writing your own search-loop"?
>
> AFAIK ruby has <assocoation <memory-structures>>.
> That mean ruby has structures which operate like association
> memories; so you can ask "what's the index of the element
> which has value "dog", in the 'structure' of strings.

irb(main):001:0> h = {'foo' => 'dog', 'bar' => 'cat'}
=> {"foo"=>"dog", "bar"=>"cat"}
irb(main):002:0> h.rassoc 'dog'
=> ["foo", "dog"]
irb(main):003:0> a = h.to_a
=> [["foo", "dog"], ["bar", "cat"]]
irb(main):004:0> a.rassoc 'dog'
=> ["foo", "dog"]

Please also have a look at the documentation (either "ri" or
http://ruby-doc.org/).

Cheers

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/