From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-10-12T12:41:04+09:00
Subject: Re: small array/hash question

On Wed, 12 Oct 2005, Kev Jackson wrote:

> Hi all,
>
> I'm trying to loop across a dataset and create a hash where each value is an 
> array so that later I can loop over the hash and for each key (it's important 
> I store the key), I can loop over the array contained and spit out some 
> results.
>
> Without looking at the docs I wanted to do something like...
>
> (in pseudo-code)
> loop across data here
> work_types[nsc_id]=do |types|
>      types << data[7]
> end
> end loop
> where work_types is the hash and types is the array I want to accumulate data 
> in
>
> This doesn't work, so I'm wondering what the ruby idiom for this kind of 
> thing would be.  Essentially for each piece of data I want to get the 
> appropriate value from the Hash and append the value on to the end of the 
> array associated with the key, or if it doesn't exist in the Hash, create a 
> new entry with a new array populated with the value.
>
> I'm sure there's a very simple way of doing this, but I can't see the method 
> I want in the standard library docs - I thought it might be collect, but it 
> doesn't look like it
>
> Thanks
> Kev

i think you want something like this:

   harp:~ > irb
   irb(main):001:0> work_types = Hash::new{|h,k| h[k] = []}
   => {}
   irb(main):002:0> work_types[ 'foo' ] << 42
   => [42]
   irb(main):003:0> work_types[ 'foo' ] << 42
   => [42, 42]
   irb(main):004:0> work_types[ 'bar' ] << 'forty-two'
   => ["forty-two"]
   irb(main):005:0> work_types
   => {"foo"=>[42, 42], "bar"=>["forty-two"]}

if not you'll have to post more about your exact problem and some sample data.

hth.

-a
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