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comp.lang.ruby

Problem Extracting Array Values

Dustin Anderson

4/4/2007 2:03:00 PM

Hi All,

I'm trying to iterate through an array and pull each value into a view
on my Rails app. The array is stored in a MySQL database.

The array is in a varchar (string) column named "blocks" with the value:
["journal", "about", "news"]

I'm trying to pull each value out one at a time.

If I try to access the array with something like this...:
<%= @blocks[0] %>

...the view returns a numeric value:
91

I'm totally confused as to why I can't extract the values out of the
array. It works fine in IRB:
irb(main):004:0> @blocks = ["journal", "about"]
=> ["journal", "about"]
irb(main):005:0> @blocks[0]
=> "journal"
irb(main):006:0>

Is there some reason why I can't get the "journal" string out of the
array?

Thanks in advance for your help!
Dustin

--
Posted via http://www.ruby-....
15 Answers

Chris Hulan

4/4/2007 2:17:00 PM

0

On Apr 4, 10:02 am, Dustin Anderson <rubyfo...@dustinanderson.com>
wrote:
> Hi All,
>
> I'm trying to iterate through an array and pull each value into a view
> on my Rails app. The array is stored in a MySQL database.
>
> The array is in a varchar (string) column named "blocks" with the value:
> ["journal", "about", "news"]
>
> I'm trying to pull each value out one at a time.
>
> If I try to access the array with something like this...:
> <%= @blocks[0] %>
>
> ..the view returns a numeric value:
> 91
>
> I'm totally confused as to why I can't extract the values out of the
> array. It works fine in IRB:
> irb(main):004:0> @blocks = ["journal", "about"]
> => ["journal", "about"]
> irb(main):005:0> @blocks[0]
> => "journal"
> irb(main):006:0>
>
> Is there some reason why I can't get the "journal" string out of the
> array?
>
> Thanks in advance for your help!
> Dustin
>
> --
> Posted viahttp://www.ruby-....

As you say, its stored as a String, and String defines [] to return
the ASCII value of the character
at the given index. If you put 91.chr into IRB you'll see it is the
'[' character.

You need to convert your String into an actual array before you can
access each element.

Maybe:
eval(@blocks)[0]

Cheers
Chris

Ryan Leavengood

4/4/2007 2:30:00 PM

0

On 4/4/07, ChrisH <chris.hulan@gmail.com> wrote:
>
> As you say, its stored as a String, and String defines [] to return
> the ASCII value of the character
> at the given index. If you put 91.chr into IRB you'll see it is the
> '[' character.
>
> You need to convert your String into an actual array before you can
> access each element.
>
> Maybe:
> eval(@blocks)[0]

That is what I surmised as well. But in general it is a bad idea to be
evaling code from a database. Security and all that.

Dustin, why are you storing those values that way? Why not have a
normalized table with a row for each? In other words you create a
blocks table, define a Block model which belongs_to whatever model you
currently use the blocks column in, and then that model will have many
blocks. Then you could just do @model.blocks.each do |block| in your
view.

Ryan

Ilan Berci

4/4/2007 2:30:00 PM

0

Dustin Anderson wrote:
> Hi All,
>
> I'm trying to iterate through an array and pull each value into a view
> on my Rails app. The array is stored in a MySQL database.
>

Dustin,

For future reference, could you please refer all rails related questions
to the rails forum.

> The array is in a varchar (string) column named "blocks" with the value:
> ["journal", "about", "news"]
>
> I'm trying to pull each value out one at a time.
>
> If I try to access the array with something like this...:
> <%= @blocks[0] %>
>
> ...the view returns a numeric value:
> 91
>

@blocks is not the type you think it is, I am taking a wild stab here
but 91 is the ascii code for "[" so I believe @blocks is a string:

irb(main):007:0> @blocks = "['journal', 'about']"
=> "['journal', 'about']"
irb(main):008:0> @blocks[0]
=> 91
irb(main):009:0>

hope this helps

ilan



--
Posted via http://www.ruby-....

Dustin Anderson

4/4/2007 2:59:00 PM

0


> Dustin, why are you storing those values that way? Why not have a
> normalized table with a row for each? In other words you create a
> blocks table, define a Block model which belongs_to whatever model you
> currently use the blocks column in, and then that model will have many
> blocks. Then you could just do @model.blocks.each do |block| in your
> view.
>
> Ryan

Thanks Chris, ilan, Ryan for the help... You got it exactly correct.

Ryan - I think you're right - I was storing the value in the database
like that because it's a variable for a Javascript app. I'm writing an
app to allow users to store the state of the view (like Google
personalized homepage or netvibes) and the javascript that I'm using
requires a v to look like this:

value = ["block1_name", "block2_name", "block3_name"]

so, if I store "value" in the database like this, I can just read it
into my javascript. Otherwise, I'll need a helper to construct the
string to look like this.

thanks again.
Dustin

Ps. sorry ilan for posting in the Ruby forum - I thought it was just a
simple ruby array question, but obviously it does have something to do
with Rails.

For the record - the javascript app i'm using for drag/drop portal is
here:
http://aymanh.com/drag-drop-portal-interface-with-scr...


--
Posted via http://www.ruby-....

Ara.T.Howard

4/4/2007 3:14:00 PM

0

Dustin Anderson

4/4/2007 4:06:00 PM

0

unknown wrote:
> On Wed, 4 Apr 2007, Dustin Anderson wrote:
>
>> Thanks Chris, ilan, Ryan for the help... You got it exactly correct.
>> into my javascript. Otherwise, I'll need a helper to construct the
>> string to look like this.
>
> not really
>
> values = ["block1_name", "block2_name", "block3_name"]
>
> javascript = "value = #{ values.inspect }"
>
> fyi.
>
> -a

is there a simple way in ruby to build an array from a string like this:

block1,block2,block3 to an array that is like this:

["block1", "block2", "block3"]

Thanks

--
Posted via http://www.ruby-....

James Gray

4/4/2007 4:11:00 PM

0

On Apr 4, 2007, at 11:05 AM, Dustin Anderson wrote:

> unknown wrote:
>> On Wed, 4 Apr 2007, Dustin Anderson wrote:
>>
>>> Thanks Chris, ilan, Ryan for the help... You got it exactly correct.
>>> into my javascript. Otherwise, I'll need a helper to construct the
>>> string to look like this.
>>
>> not really
>>
>> values = ["block1_name", "block2_name", "block3_name"]
>>
>> javascript = "value = #{ values.inspect }"
>>
>> fyi.
>>
>> -a
>
> is there a simple way in ruby to build an array from a string like
> this:
>
> block1,block2,block3 to an array that is like this:
>
> ["block1", "block2", "block3"]

Sure:

>> "block1,block2,block3".split(",")
=> ["block1", "block2", "block3"]

James Edward Gray II

Brian Candler

4/4/2007 5:34:00 PM

0

On Thu, Apr 05, 2007 at 01:05:44AM +0900, Dustin Anderson wrote:
> is there a simple way in ruby to build an array from a string like this:
>
> block1,block2,block3 to an array that is like this:
>
> ["block1", "block2", "block3"]

I always thought that Object#inspect could be considered as a (crude) form
of object serialisation, and it would be really useful to have a reverse
"uninspect" operation to recreate the object from it again. Has anyone
written such a parser?

Alex Young

4/4/2007 5:42:00 PM

0

Brian Candler wrote:
> On Thu, Apr 05, 2007 at 01:05:44AM +0900, Dustin Anderson wrote:
>> is there a simple way in ruby to build an array from a string like this:
>>
>> block1,block2,block3 to an array that is like this:
>>
>> ["block1", "block2", "block3"]
>
> I always thought that Object#inspect could be considered as a (crude) form
> of object serialisation, and it would be really useful to have a reverse
> "uninspect" operation to recreate the object from it again. Has anyone
> written such a parser?
>
For the basic types, eval will do it to a tolerable degree. For
everything else, there's YAML...

--
Alex

Gavin Kistner

4/4/2007 6:03:00 PM

0

On Apr 4, 11:34 am, Brian Candler <B.Cand...@pobox.com> wrote:
> On Thu, Apr 05, 2007 at 01:05:44AM +0900, Dustin Anderson wrote:
> > is there a simple way in ruby to build an array from a string like this:
>
> > block1,block2,block3 to an array that is like this:
>
> > ["block1", "block2", "block3"]
>
> I always thought that Object#inspect could be considered as a (crude) form
> of object serialisation, and it would be really useful to have a reverse
> "uninspect" operation to recreate the object from it again. Has anyone
> written such a parser?

irb(main):001:0> a1 = ["foo",/bar/,42,false,nil]
=> ["foo", /bar/, 42, false, nil]
irb(main):002:0> s = a1.inspect
=> "[\"foo\", /bar/, 42, false, nil]"
irb(main):003:0> a2 = eval(s)
=> ["foo", /bar/, 42, false, nil]
irb(main):004:0> a1 == a2
=> true

So:

class String
def uninspect
eval(self)
end
end

:)