From: 7stud -- <bbxx789_05ss@...>
Date: 2008-01-29T04:51:26+09:00
Subject: Re: Assistance dynamically building a nested hash

Matthew Williams wrote:
> I've done some searching and have found some nested hash references but
> not quite enough to get me going with what I need.
> 
> I'm looking to build a structure like so...
> 
> actuals = {actual_id, {date => count, date => count, date => count}}
> 
> An example would be like:
> 
> actuals = {"1", {"01-01-2008" => 5, "01-02-2008" => 10}}
> 
> Then I can later iterate through the hash and for each ID, get any date
> associated with it an associated count.
> 
> I'm pulling the data in with an ActiveRecord find that will return a
> dozen or so records for a given id but with various dates and counts.
> 
> So records returned could look like
> 
> 1, "01-02-2008", 5
> 1, "01-03-2008", 10
> 2, "12-25-2007", 5
> 1, "01-04-2008", 15
> 
> Should result in a hash when I'm finished like so:
> 
> actuals =
> {"1",{"01-02-2008" => 5, "01-03-2008" => 10 "01-04-2008" => 15}},
> {"2",{"12-25-2007" => 5}}
> 
> Iterating through those records is no problem...  I just can't wrap my
> brain around the nested hash of dates and counts for a given id.
> 
> I'm assuming this is the appropriate and most effective data structure
> for this data but I would be up for any other suggestions.
> 
> I appreciate any responses, thanks.

arr = [
[1, "01-02-2008", 5],
[1, "01-03-2008", 10],
[2, "12-25-2007", 5],
[1, "01-04-2008", 15]
]


#Create a hash where looking up a non-existent key
#in the hash results in the key being created and
#assigned an empty hash:
results = Hash.new do |hash, key|
  hash[key] = {}
end

arr.each do |sub_arr|
  main_key = sub_arr[0]
  sub_key = sub_arr[1]

  #Create new key, value in sub hash:
  results[main_key][sub_key] = sub_arr[2]
end

p results

--output:--
{1=>{"01-04-2008"=>15, "01-03-2008"=>10, "01-02-2008"=>5}, 
2=>{"12-25-2007"=>5}}
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