From: William James <w_a_x_man@...>
Date: 2006-12-20T06:55:10+09:00
Subject: Re: ruby puzzle: Group candies by unique record fields

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
>
> ----------------
> ##########'
> ---
> good:
> - :taste: good
>    :name: a
>    :color: blue
> - :taste: good
>    :name: e
>    :color: green
> yuck:
> - :taste: yuck
>    :name: b
>    :color: blue
> - :taste: yuck
>    :name: d
>    :color: blue
> - :taste: yuck
>    :name: f
>    :color: green
> ok:
> - :taste: ok
>    :name: c
>    :color: red
> ##########'
> ##########'
> ---
> green:
> - :taste: good
>    :name: e
>    :color: green
> - :taste: yuck
>    :name: f
>    :color: green
> blue:
> - :taste: good
>    :name: a
>    :color: blue
> - :taste: yuck
>    :name: b
>    :color: blue
> - :taste: yuck
>    :name: d
>    :color: blue
> red:
> - :taste: ok
>    :name: c
>    :color: red
> ##########'


$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 property
  values = $candies.inject([]){|ary,hash| ary << hash[property] }.uniq
  values.sort.each{|val|   puts val
    $candies.select{|h| h[property] == val}.each{|h|
      puts "  " + h.to_a.reject{|k,v| k == property }.
        map{|k,v| "#{k}: #{v}"}.join( "; " ) }
  }
end

print_candies_by :color

---  output  -----
blue
  name: a; taste: good
  name: b; taste: yuck
  name: d; taste: yuck
green
  name: e; taste: good
  name: f; taste: yuck
red
  name: c; taste: ok