From: James Edward Gray II <james@...>
Date: 2006-12-20T03:43:40+09:00
Subject: Re: ruby puzzle: Group candies by unique record fields

On Dec 19, 2006, at 10:30 AM, Brad Phelan wrote:

> Woga Swoga wrote:
>> I have an list of objects (Candy) and each object has two fields
>> (Candy.color, Candy.taste).  I would like to display the candies but
>> group them based on the fields (display a header for each group).   
>> The
>> problem is I don't know how many colors or tastes are in any  
>> particular
>> list of candies.
>> This is what I have for input:
>> * Candy  <-- hash list already pre-sorted by "group"
>> * group  <-- variable contains either "color" or "taste"
>> Can anyone come up with a ruby code snipet that will use the "group"
>> variable to extract out the group labels (unique values of the  
>> color or
>> tate field), and then dump out the Candy list by group.
>> Really appreciate your help!
>
> require 'yaml'
>
> @candies = [
>     { :name => 'a', :color => "blue", :taste => "good" },
>     { :name => 'b',:color => "blue", :taste => "yuck" },
>     { :name => 'c',:color => "red", :taste => "ok" },
>     { :name => 'd',:color => "blue", :taste => "yuck" },
>     { :name => 'e',:color => "green", :taste => "good" },
>     { :name => 'f',:color => "green", :taste => "yuck" }
> ]
>
> def print_candies_by(group)
>     groups={}
>     @candies.each do |candy|
>         key = candy[group]
>         groups[key] = [] unless groups[key]
>         groups[key] << candy
>     end
>
>     puts "##########'"
>     puts YAML.dump groups
>     puts "##########'"
> end
>
>
> print_candies_by :taste
> print_candies_by :color

You can also use sets for this:

 >> require "set"
=> true
 >> candies = [
?>     { :name => 'a', :color => "blue", :taste => "good" },
?>     { :name => 'b',:color => "blue", :taste => "yuck" },
?>     { :name => 'c',:color => "red", :taste => "ok" },
?>     { :name => 'd',:color => "blue", :taste => "yuck" },
?>     { :name => 'e',:color => "green", :taste => "good" },
?>     { :name => 'f',:color => "green", :taste => "yuck" }
 >> ]
=> [{:color=>"blue", :taste=>"good", :name=>"a"},  
{:color=>"blue", :taste=>"yuck", :name=>"b"},  
{:color=>"red", :taste=>"ok", :name=>"c"},  
{:color=>"blue", :taste=>"yuck", :name=>"d"},  
{:color=>"green", :taste=>"good", :name=>"e"},  
{:color=>"green", :taste=>"yuck", :name=>"f"}]
 >> candies.to_set.classify { |c| c[:color] }
=> {"green"=>#<Set: {{:color=>"green", :taste=>"yuck", :name=>"f"},  
{:color=>"green", :taste=>"good", :name=>"e"}}>, "blue"=>#<Set:  
{{:color=>"blue", :taste=>"good", :name=>"a"},  
{:color=>"blue", :taste=>"yuck", :name=>"d"},  
{:color=>"blue", :taste=>"yuck", :name=>"b"}}>, "red"=>#<Set:  
{{:color=>"red", :taste=>"ok", :name=>"c"}}>}

James Edward Gray II