Asp Forum - Accessing a hash -- Beginner

don

11/3/2006 11:03:00 PM

I want to access a hash via a gets command. A simplified
example, for a hash named, "test":

print 'hash name: '
hash_var = gets.chomp # enter 'test' here

puts hash_var # <-- nil
puts test # <-- the contents of the hash

One problem I see is hash_var is class String, while test is
class Hash. I cannot figure out how to make hash_var class
Hash. I'm not even sure if I am on the right track. I
would appreciate any help.

Thanks in advance,

Don

10 Answers

Robert Klemme

11/3/2006 11:17:00 PM

don wrote:
> I want to access a hash via a gets command. A simplified
> example, for a hash named, "test":
>
> print 'hash name: '
> hash_var = gets.chomp # enter 'test' here
>
> puts hash_var # <-- nil
> puts test # <-- the contents of the hash
>
> One problem I see is hash_var is class String, while test is
> class Hash. I cannot figure out how to make hash_var class
> Hash. I'm not even sure if I am on the right track. I
> would appreciate any help.

There is not a single Hash instance in your code. Also "test" is not
set, hence it's interpreted as a method call:

$ ruby -e " print 'hash name: '
> hash_var = gets.chomp # enter 'test' here
>
> puts hash_var # <-- nil
> puts test # <-- the contents of the hash
> "
hash name: foo
foo
-e:5:in `test': wrong number of arguments (ArgumentError)
from -e:5

What is your problem? What are you trying to achieve?

Regards

robert

dblack

11/3/2006 11:18:00 PM

Tom Werner

11/3/2006 11:28:00 PM

don wrote:
> I want to access a hash via a gets command. A simplified
> example, for a hash named, "test":
>
> print 'hash name: '
> hash_var = gets.chomp # enter 'test' here
>
> puts hash_var # <-- nil
> puts test # <-- the contents of the hash
>
> One problem I see is hash_var is class String, while test is
> class Hash. I cannot figure out how to make hash_var class
> Hash. I'm not even sure if I am on the right track. I
> would appreciate any help.

The trick is that you want the variable named test, while the return
from gets is a string. You can use eval to evaluate a string in the
current context, so this works (but is VERY dangerous, read on):

test = {:foo => 'bar'}
p eval('test')
#=> {:foo=>"bar"}

This approach will execute any Ruby code that happens to be typed in by
the user, which is obviously bad:

p eval('test = nil')
p test
#=> nil

One approach might be to gsub out any non word characters (but this
still makes me a bit queasy):

p eval('test'.gsub(/\W/, ''))
#=> {:foo=>"bar"}

p eval('test = nil'.gsub(/\W/, ''))
NameError: undefined local variable or method `testnil' for main:Object
from (irb):11
from (irb):11

Hope this helps.

Tom

Tom Werner

11/3/2006 11:33:00 PM

Tom Werner wrote:
> don wrote:
>> I want to access a hash via a gets command. A simplified example,
>> for a hash named, "test":
>>
>> print 'hash name: '
>> hash_var = gets.chomp # enter 'test' here
>>
>> puts hash_var # <-- nil
>> puts test # <-- the contents of the hash
>> One problem I see is hash_var is class String, while test is
>> class Hash. I cannot figure out how to make hash_var class
>> Hash. I'm not even sure if I am on the right track. I
>> would appreciate any help.
>
> One approach might be to gsub out any non word characters (but this
> still makes me a bit queasy):
>
> p eval('test'.gsub(/\W/, ''))
> #=> {:foo=>"bar"}
>
On further consideration, even this is futile. Consider:

p eval('exit')

Which leaves you back on the command line. What you want to do is create
a Hash that contains the hash you are interested in:

test = {:foo => 'bar'}
shelf = {'test' => test}

Now you can look up the Hash of interest by name:

p shelf['test']
#=> #=> {:foo=>"bar"}

eval is dangerous. VERY DANGEROUS.

Tom

don

11/4/2006 4:33:00 AM

On 2006-11-03, Robert Klemme wrote:

[...]

>
> There is not a single Hash instance in your code. Also "test" is not
> set, hence it's interpreted as a method call:
>
> $ ruby -e " print 'hash name: '
> > hash_var = gets.chomp # enter 'test' here
> >
> > puts hash_var # <-- nil
> > puts test # <-- the contents of the hash
> > "
> hash name: foo
> foo
> -e:5:in `test': wrong number of arguments (ArgumentError)
> from -e:5
>
> What is your problem? What are you trying to achieve?
>

Robert, thanks for the response. Part of my problem is I
did not communicate my problem very well. I will try again
a little later.

Don

don

11/4/2006 4:36:00 AM

On 2006-11-03, dblack@wobblini.net wrote:
>
> Do you want to set a hash key, or retrieve a value using an existing
> key? For example:
>
> test = { "one" => 1, "two" => 2 }
> hash_key = gets.chomp
> puts test[hash_key]
>
> If you input "one", the program will print 1.
>
>
I want to access the hash, then print part of the contents.
I am going to restate my problem -- hopefully a little
clearer -- later.

Thanks for the response, David.

Don

don

11/4/2006 4:40:00 AM

On 2006-11-03, Tom Werner wrote:
> Tom Werner wrote:

[...]

>> One approach might be to gsub out any non word characters (but this
>> still makes me a bit queasy):
>>
>> p eval('test'.gsub(/\W/, ''))
>> #=> {:foo=>"bar"}
>>
> On further consideration, even this is futile. Consider:
>
> p eval('exit')
>
> Which leaves you back on the command line. What you want to do is create
> a Hash that contains the hash you are interested in:
>
> test = {:foo => 'bar'}
> shelf = {'test' => test}
>
> Now you can look up the Hash of interest by name:
>
> p shelf['test']
> #=> #=> {:foo=>"bar"}
>
> eval is dangerous. VERY DANGEROUS.
>
> Tom

Thanks Tom. I will skip eval for now. I am going to repose
my question as I did not do a very good job the first time.

Don

don

11/4/2006 4:59:00 AM

I think I did a poor job of communicating my problem. I do
not think it is a complicated one, although it might be. I
know very little about programming.

I have 32 hashes. I would like to key in a hash name and
extract data from it. Like this:

Enter team: (Enter 'ari', for example)
team_var = gets.chomp
puts team_var['coach']

Above does not work. For one thing, ari is actually $ari.
team_var = '$' + team_var does not work either.

So simply put, how do you call a hash by name interactively?

Below is an example of what my code would look like:

$ari = {
'name' => 'Arizona Cardinals',
'team_notes' => 'skank team',
'qb' => 'Matt Leinart, Kurt Warner',
'qb_rank' => '',
'cbs' => '',
'espn' => '',
'players' => 'rb Edgerrin James',
'coach' => 'Denny Green',
'weekly_notes' => ' wk01 Fitzgerald 133 yds.'
}

print 'team: '
team = gets.chomp
team = '$' + team
puts team['coach']

Thanks in advance for your help.

Don

Jim Marshall

11/4/2006 7:00:00 AM

On 2006-11-04, don <donsdx@gmailSPAMBAD.invalid> wrote:
>
> I have 32 hashes. I would like to key in a hash name and
> extract data from it. Like this:
>
> Enter team: (Enter 'ari', for example)
> team_var = gets.chomp
> puts team_var['coach']

You could stick (or create from the beginning) those hashes into another
hash, say "teams," and then you'll be able to get them by indexing
"teams" with user input.

>
> Above does not work. For one thing, ari is actually $ari.
> team_var = '$' + team_var does not work either.
>
> So simply put, how do you call a hash by name interactively?
>
> Below is an example of what my code would look like:
>
> $ari = {
> 'name' => 'Arizona Cardinals',
> 'team_notes' => 'skank team',
> 'qb' => 'Matt Leinart, Kurt Warner',
> 'qb_rank' => '',
> 'cbs' => '',
> 'espn' => '',
> 'players' => 'rb Edgerrin James',
> 'coach' => 'Denny Green',
> 'weekly_notes' => ' wk01 Fitzgerald 133 yds.'
> }
>

teams = {} # Create a new hash to store the individual team hashes
teams['ari'] = $ari

> print 'team: '
> team = gets.chomp
then change the above^ to
team = teams[gets.chomp]
and you can proceed with

> puts team['coach']
>

You'll still want some error-checking (what if the user enters
'akaskdfj'?), of course.

You can also now access the elements of the individual teams like
"teams['ari']['coach']" if you want, although it will often be less
cluttered-looking if you pull a reference to the individual team out
before you go to work on it, as "team = teams[gets.chomp]" does.

don

11/4/2006 4:39:00 PM

On 2006-11-03, Jim Marshall wrote:
> On 2006-11-04, don <donsdx@gmailSPAMBAD.invalid> wrote:
>>
>> I have 32 hashes. I would like to key in a hash name and
>> extract data from it. Like this:
>>
>> Enter team: (Enter 'ari', for example)
>> team_var = gets.chomp
>> puts team_var['coach']
>
> You could stick (or create from the beginning) those hashes into another
> hash, say "teams," and then you'll be able to get them by indexing
> "teams" with user input.

[...]

> teams = {} # Create a new hash to store the individual team hashes
> teams['ari'] = $ari
>
>> print 'team: '
>> team = gets.chomp
> then change the above^ to
> team = teams[gets.chomp]
> and you can proceed with
>
>> puts team['coach']
>>
>
> You'll still want some error-checking (what if the user enters
> 'akaskdfj'?), of course.
>
> You can also now access the elements of the individual teams like
> "teams['ari']['coach']" if you want, although it will often be less
> cluttered-looking if you pull a reference to the individual team out
> before you go to work on it, as "team = teams[gets.chomp]" does.

Excellent, Jim. That's what I will do.

Thak you. Take care.

Don

comp.lang.ruby

Accessing a hash -- Beginner

don

Robert Klemme

dblack

Tom Werner

Tom Werner

don

don

don

don

Jim Marshall

don

x Login to ForumsZone