Forum: Ruby Strange question: Convert string to array name

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76be6c03fa71b65d67bd1848539a08ce?d=identicon&s=25 kenbo (Guest)
on 2007-02-20 01:21
(Received via mailing list)
I am coming to Ruby from LISP where I was more competent when it came
to symbol
manipulation :-)   I have spent some time trying to solve this problem
and figure it's my
general lack of deep knowledge ala Ruby that keeps me from seeing an
"easy" solution.

With that said, I apologize if this has been answered and I missed
it.

I have a string in a variable.
foo = "bobo"

I want to use foo to access an array called bobo.   I will have bobo
defined already.

Is there a way to do this?

Take foo and use it to access bobo[2], for example.

I thought about turning foo into a symbol, but that wasn't the way.
And, I think there
should be a way to ask Ruby to return an object via its string name,
but I am
missing the way.

any advice would be appreciated.


kenny
8dbdbce510486cd57d20f8aadd727528?d=identicon&s=25 Stephen Duncan (Guest)
on 2007-02-20 01:57
(Received via mailing list)
I'm still pretty much a newbie, but my first thought that works is:

eval('bobo')[2]

-Stephen
A24e072d6092870feff0d5016ff2cdd0?d=identicon&s=25 Aaron Patterson (Guest)
on 2007-02-20 02:00
(Received via mailing list)
On Tue, Feb 20, 2007 at 09:20:13AM +0900, kenbo wrote:
> I have a string in a variable.
> foo = "bobo"
>
> I want to use foo to access an array called bobo.   I will have bobo
> defined already.
>
> Is there a way to do this?

eval() might be what you're looking for.  You can use eval to return the
array then index in to it.  Here's an example from:

irb(main):001:0> awesome_array = %w{ one two three four five }
=> ["one", "two", "three", "four", "five"]
irb(main):002:0> foo = 'awesome_array'
=> "awesome_array"
irb(main):003:0> puts eval(foo)[1]
two
=> nil
irb(main):004:0>

Hope that helps!
76be6c03fa71b65d67bd1848539a08ce?d=identicon&s=25 kenbo (Guest)
on 2007-02-20 02:10
(Received via mailing list)
On Feb 19, 7:59 pm, Aaron Patterson <aaron_patter...@speakeasy.net>
wrote:
>
> irb(main):001:0> awesome_array = %w{ one two three four five }
> --
> Aaron Pattersonhttp://tenderlovemaking.com/- Hide quoted text -
>
> - Show quoted text -

Thanks for the folks that mentioned eval---I thought of that after the
posting but
assumed that, as in LISP, there might be a better way to accomplish
it :-)

It's nice to see more similarities between LISP and Ruby.

kenny
7b4707f974af261f71943e1f2046c9ee?d=identicon&s=25 SonOfLilit (Guest)
on 2007-02-20 02:47
(Received via mailing list)
There should be, also I don't remember it.

For all kinds of variables except for local I know the ways, but local
elludes me :)

Aur Saraf

PLUG: http://rubymentor.rubyforge.org/wiki/wiki.pl
F3b02532d4cb4855881935c002389213?d=identicon&s=25 Morton Goldberg (Guest)
on 2007-02-20 03:12
(Received via mailing list)
On Feb 19, 2007, at 8:10 PM, kenbo wrote:

> Thanks for the folks that mentioned eval---I thought of that after the
> posting but assumed that, as in LISP, there might be a better way
> to accomplish
> it :-)
>
> It's nice to see more similarities between LISP and Ruby.

I don't know whether or not you will think this better than using
'eval', but in Ruby this kind of indirect reference problem can often
be handled by introducing a hash. For example,

<code>
a = %w{ one two three four five }
b = %w{ six seven eight nine }
h = {}
h['a'] = a
h['b'] = b
foo = 'a'
h[foo][2] # => "three"
foo = 'b'
h[foo][2] # => "eight"
</code>

Regards, Morton
E7559e558ececa67c40f452483b9ac8c?d=identicon&s=25 Gary Wright (Guest)
on 2007-02-20 03:15
(Received via mailing list)
On Feb 19, 2007, at 7:20 PM, kenbo wrote:
> I want to use foo to access an array called bobo.   I will have bobo
> defined already.

This type of question seems to come up periodically on the list but
I never seem to run into in while coding.  I tend to think that in most
(but not all) cases the need to reach for eval indicates some larger
design issue.

In your case, I would ask why you are resorting to using several local
variables that you need to distinguish by name rather than simply using
a hash to organize things?

arrays = {}
array[:bobo] = [1,2,3]
array[:foo] = [4,5,6]

array[:foo][2]     # 5

Perhaps if you gave the list the 'bigger' picture they could suggest
a solution that doesn't require 'eval'.

Gary Wright
703fbc991fd63e0e1db54dca9ea31b53?d=identicon&s=25 Robert Dober (Guest)
on 2007-02-20 11:11
(Received via mailing list)
On 2/20/07, SonOfLilit <sonoflilit@gmail.com> wrote:
> > On Feb 19, 7:59 pm, Aaron Patterson <aaron_patter...@speakeasy.net>
> > > > it.
> > >
> > >
> > > --
> > > Aaron Pattersonhttp://tenderlovemaking.com/- Hide quoted text -
> > >
> > > - Show quoted text -
> >
> > Thanks for the folks that mentioned eval---I thought of that after the
> > posting but
> > assumed that, as in LISP, there might be a better way to accomplish
> > it :-)
Are you thinking about Ma****, do not mention it anymore on this list ;)
Well it is not really the way of Ruby.
> >
> > It's nice to see more similarities between LISP and Ruby.
> >
> > kenny
> >
> >
> >
>
>
There is if you can get away from the local variable as somebody
mentioned without sharing his wisdom with us ;)

If we want to access an array @bobo there is

instance_variable_get( "@'" << foo.to_s ).first

and all kind of variations.

Cheers
Robert
F8634aca904bc63cb047cb1bd93bdc74?d=identicon&s=25 Evan Weaver (eweaver)
on 2007-02-20 12:23
It's very unusual to need to dynamically reference a local variable. In
Ruby, local variables usually are highly, er, localized. An instance
variable is much more frequently used in the way you describe, and you
can access it, as Robert says, like so:

>> @foo = "the value"
  => "the value"
>> name = "foo"
  => "foo"
>> instance_variable_get("@#{name}")
  => "the value"

Evan Weaver
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