Extract Weight as a value object

app/models/patient.rb

@@ -24,13 +24,8 @@ def full_name
   end
 
   def weight
-    if observations.map(&:code_display).include?("Body Weight")
-      body_weight_observation = [observations.select{|observation| observation.code_display == "Body Weight"}].flatten.sort_by(&:date).last
-      weight = "#{body_weight_observation.value} #{body_weight_observation.units}"
-    else
-      weight = "N/A"
-    end
-    weight
+    body_weight_observation = observations.select { |observation| observation.code_display == "Body Weight"}
+    Weight.new(body_weight_observation).to_s
   end
 
   def birthday

app/models/weight.rb

@@ -0,0 +1,12 @@
+class Weight
+  def initialize(observation)
+    return unless observation.present?
+    @weight = observation.value
+    @unit   = observation.units
+  end
+
+  def to_s
+    return 'N/A' unless @weight.present?
+    "#{@weight} #{@unit}"
+  end
+end