Ruby で Crfsuite::ItemSequence を作成する処理を 2 倍以上速くした

diff --git a/script b/script
index 7dc1e06..066dbf8 100644
--- a/script
+++ b/script
@@ -28,6 +28,11 @@ FEATURE_TEMPLATES = [
   [[ 0, 1], [ 1, 1], [2, 1]],
 ].freeze
 
+FEATURE_TEMPLATES_WITH_ATTR_NAME = FEATURE_TEMPLATES.map { |template|
+  [template, template.map{ |row, col| "x[#{row},#{col}]" }.join('|')]
+}.freeze
+
+
 class Trainer < Crfsuite::Trainer
   def message(s)
     print s
@@ -74,37 +79,33 @@ def tag(model_file)
 end
 
 def build_sequence(items)
-  xseq = Crfsuite::ItemSequence.new
-  names = []
-  values = []
+  citems = []
   items.size.times do |offset|
-    item = Crfsuite::Item.new
-    FEATURE_TEMPLATES.each do |template|
-      names.clear
-      values.clear
+    attrs = []
+    FEATURE_TEMPLATES_WITH_ATTR_NAME.each do |template, attr_name|
+      values = ''
       available_feature = true
-      template.each do |field|
-        idx = offset + field[0]
+      template.each do |row, col|
+        idx = offset + row
         if idx < 0 || idx >= items.size
           available_feature = false
           break
         end
-        value = items[idx][field[1]]
+        value = items[idx][col]
         if value.nil?
           available_feature = false
           break
         end
-        names << 'x[%d,%d]' % field
-        values << value
+        values << (values.empty? ? value : "|#{value}")
       end
       next unless available_feature
-      item << Crfsuite::Attribute.new("#{names.join('|')}=#{values.join('|')}")
+      attrs << Crfsuite::Attribute.new("#{attr_name}=#{values}")
     end
-    item << Crfsuite::Attribute.new('__BOS__') if offset.zero?
-    item << Crfsuite::Attribute.new('__EOS__') if offset == items.size - 1
-    xseq << item
+    attrs << Crfsuite::Attribute.new('__BOS__') if offset.zero?
+    attrs << Crfsuite::Attribute.new('__EOS__') if offset == items.size - 1
+    citems << Crfsuite::Item.new(attrs)
   end
-  xseq
+  Crfsuite::ItemSequence.new(citems)
 end
 
 case params['command']