How to further refactor a ruby hash

Question

I'm writing a function that takes a string and returns a corresponding model class. The old version consists of ugly case statements, and the refactored version has a less-ugly hash. However the hash still feels repetitive to me. Could you give me some advice?

# original function

def determine_node_label(category)
  label = 
    case category 
    when 'boundary box'
      Slide
    when 'circle', 'rectangle'
      GroupBox
    when 'text'
      Text
    when 'picture', 'pie', 'bar' , 'trend', 'star'
      Content
    else
      Content
    end
  return label 
end

# refactored function

def determine_node_label(category)
  label = {
    "boundary box" => Slide,
    "circle" => GroupBox,
    "rectangle" => GroupBox,
    "text" => Text,
    "picture" => Content,
    "pie" => Content,
    "bar" => Content,
    "trend" => Content,
    "star" => Content
  }
  label.default = Content
  return label["category"]
end

update:

I would be more interested in solutions that assume that the label.default is subject to change. My apologies for not making this clear in the code.

Answer 1

What about this?

LABELS = {
  "boundary box" => Slide,
  "circle"       => GroupBox,
  "rectangle"    => GroupBox,
  "text"         => Text
} 

def determine_node_label(category)
  LABELS[category] || Content
end

Answer 2

If you do want the dynamic default value, you can use Hash.fetch . Also, pass the default value as the method parameter.

LABELS = {
  "boundary box" => Slide,
  "circle"       => GroupBox,
  "rectangle"    => GroupBox,
  "text"         => Text
} 

def determine_node_label(category, default = 'Content')
  LABELS.fetch(category, default)
end

Answer 3

For ease of maintainability I suggest the data be maintained in the following hash.

DATA = {
  %w| boundary\ box |              => 'Slide',
  %w| circle rectangle |           => 'GroupBox',
  %w| text |                       => 'Text',
  %w| picture pie bar trend star | => 'Content'
}
  #=> {["boundary box"]=>"Slide", ["circle", "rectangle"]=>"GroupBox",
  #    ["text"]=>"Text", ["picture", "pie", "bar", "trend", "star"]=>"Content"}

Note that I made the values literals (strings) to demonstrate how this hash will be manipulated. In the actual application the values would not necessarily be literals.

Then provide a method to create the desired hash h from DATA and a specified default value (the latter to be returned by h[k] when h does not have a key k ).

def data_to_hash(data, default)
  data.each_with_object({}) { |(k,v),h| k.each { |obj| h[obj] = v } }.
       tap { |h| h.default = default }
end

This might be used as follows.

h = data_to_hash(DATA, 'Cat')
  #=> {"boundary box"=>"Slide", "circle"=>"GroupBox",
  #    "rectangle"=>"GroupBox", "text"=>"Text", "picture"=>"Content",
  #    "pie"=>"Content", "bar"=>"Content", "trend"=>"Content",
  #    "star"=>"Content"}
h["boundary box"]
  #=> "Slide"
h["pie"]
  #=> "Content"
h["cake"]
  #=> "Cat"

To subsequently change the default you could either call data_to_hash again, with the revised default, or simply execute

h.default = "Dog"

or wrap the latter in a method.

def change_default(h, new_default)
  h.default = new_default
end

change_default(h, "Dog")
  #=> "Dog"
h["pie"]
  #=> "Content"
h["cake"]
  #=> "Dog"