# Hash of Hash of Arrays Question **URL:** \ **Category:** Ruby\ **Created:** [July 18, 2009, 3:24pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282 "2009-07-18T15:24:10Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![elricstorm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/da6949/32.png) [@elricstorm](https://www.ruby-forum.com/u/elricstorm)\ **Post date:** [July 18, 2009, 3:24pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282/1 "2009-07-18T15:24:10Z")
Hi all, I decided to take a deep look into hashes today and how hashes of arrays are handled. This is a bit of a grasp for me because most of the languages I’ve worked with, arrays are handled in just a few ways. With Ruby, it’s much better. So, here are my questions using an example scenario I’m creating from scratch. Creating a new Hash: myhash = Hash.new {|h,k| h[k] = {} } myhash.class =\> Hash Creating two Arrays: mykeyarray = Array. =\> [1, 2, 3, 4, 5] myvaluearray = Array. =\> [10, 20, 30, 40, 50] 5.times do |i| myhash[mykeyarray[i]][:numbers] = myvaluearray[i] end myhash.keys =\> [5, 1, 2, 3, 4] myhash.values =\> [{:numbers=\>50}, {:numbers=\>10}, {:numbers=\>20}, {:numbers=\>30}, {:numbers=\>40}] myhash.inspect =\> “{5=\>{:numbers=\>50}, 1=\>{:numbers=\>10}, 2=\>{:numbers=\>20}, 3=\>{:numbers=\>30}, 4=\>{:numbers=\>40}}” So, I would believe that this is a hash of hashes of arrays correct? Secondly, how would I parse information out of this hash? Creating them is easy. Extracting exactly the way I want - not so easy. Let me give you an example: I create a constant that stores the symbol I want to use for my table. MY\_TABLE\_FIELD = [:numbers] myhash.each do |key| values = {:compiled\_on =\> Date.today.strftime(’%Y-%m-%d’)} MY\_TABLE\_FIELD.each\_with\_index do |field, i| values[field] = key[i] end model.create values end … this won’t work … I want to match the symbol in my hash with the symbol in my constant (which represents the table field). I want to update the table field with the value of the hash (10,20,30,40,50). They hash key would represent the id field (1,2,3,4,5). How can I accomplish this given the information provided? ---
**Author:** ![elricstorm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/da6949/32.png) [@elricstorm](https://www.ruby-forum.com/u/elricstorm)\ **Post date:** [July 18, 2009, 4:50pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282/2 "2009-07-18T16:50:19Z")
I performed the following test which got some of the results from this hash of hashes… myhash.each\_pair do |k,v| puts “My key is #{k}.” v.each\_pair do |key, value| puts “Inner Key = #{key} and Inner Value = #{value}” end end returns… My key is 5. Inner Key = numbers and Inner Value = 50 My key is 5numbers50. My key is 3numbers30. My key is 1. Inner Key = numbers and Inner Value = 10 My key is . My key is 4numbers40. My key is 2. Inner key = numbers and Inner Value = 20 My key is 1numbers10. My key is 3. Inner key = numbers and Inner Value = 30 My key is 4. Inner Key = numbers and Inner Value = 40 My key is 2numbers20. I don’t want this… I want… My key is 5. Inner Key = numbers and Inner Value = 50 My key is 1. Inner Key = numbers and Inner Value = 10 My key is 2. Inner key = numbers and Inner Value = 20 My key is 3. Inner key = numbers and Inner Value = 30 My key is 4. Inner Key = numbers and Inner Value = 40 ---
**Author:** ![elricstorm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/da6949/32.png) [@elricstorm](https://www.ruby-forum.com/u/elricstorm)\ **Post date:** [July 18, 2009, 4:58pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282/3 "2009-07-18T16:58:23Z")
Okay, I was pretty close… I figured this part out: myhash.each\_pair do |k,v| v.each\_pair do |key, value| puts “Key = #{k} and Inner Key = #{key} and Inner Value = #{value}” end end Returns: Key = 5 and Inner Key = numbers and Inner Value = 50 Key = 1 and Inner Key = numbers and Inner Value = 10 Key = 2 and Inner Key = numbers and Inner Value = 20 Key = 3 and Inner Key = numbers and Inner Value = 30 Key = 4 and Inner Key = numbers and Inner Value = 40 So, that answers one part of my question… Now I have to figure out how to match this up to my constant fields… ---
**Author:** ![elricstorm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/da6949/32.png) [@elricstorm](https://www.ruby-forum.com/u/elricstorm)\ **Post date:** [July 18, 2009, 6:43pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282/4 "2009-07-18T18:43:01Z")
Well I’ve spent several hours on this and can’t figure out how to get everything matched up. I think the issue really comes down to the constant is an array of values and I’m comparing it to a hash which is a paired key+value… Therefore, I would probably have to convert my constant to a hash before using it with this. In any event, I’ll stick with my original method although it’s quite a bit sloppy looking… But,… myhash.each\_pair do |k,v| v.each\_pair do |key, value| puts “Key = #{k} and Inner Key = #{key} and Inner Value = #{value}” end end Does find exactly what I need for any future needs when required. So, at least I learned something. Now if I could just figure out how to sort a hash… ---
**Author:** ![elricstorm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/da6949/32.png) [@elricstorm](https://www.ruby-forum.com/u/elricstorm)\ **Post date:** [July 18, 2009, 9:36pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282/5 "2009-07-18T21:36:17Z")
Thanks Gary, I’d much rather be using 1.9.1 but unfortunately I have to stay with 1.8 for now. I’ll eventually make the switch when some gems/plugins I use move forward. Thanks! ---
**Author:** ![elricstorm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/da6949/32.png) [@elricstorm](https://www.ruby-forum.com/u/elricstorm)\ **Post date:** [July 18, 2009, 7:57pm UTC](https://www.ruby-forum.com/t/hash-of-hash-of-arrays-question/172282/6 "2009-07-18T19:57:41Z")
On Jul 18, 2009, at 12:43 PM, Älphä Blüë wrote: > Does find exactly what I need for any future needs when required. So, > at least I learned something. Now if I could just figure out how to > sort a hash… Prior to Ruby 1.9, hashes are unsorted. In Ruby 1.9, hashes are maintained in insertion order. That is to say, if you iterate over the hash you’ll get the key/value pairs in the order in which they were inserted into the hash. If you want to iterate over a hash according to some other order you’ll need to do something like: hash = {2=\>1, 1=\>0, 3=\>4} hash.sort\_by {|k,v| k }.each { |k,v| puts “key: #{k}, value: #{v}” } key: 1, value: 0 key: 2, value: 1 key: 3, value: 4 Note that sort\_by doesn’t return a hash but instead returns an array of key/value pairs: > > hash.sort\_by { |k,v| v } > > =\> [[1, 0], [2, 1], [3, 4]] Gary W.