Calculate pandas categorical hash once. (#12)

Author: glogiotatidis

lib/lightgbm/booster.rb

@@ -269,7 +269,8 @@ def load_pandas_categorical(file_name: nil, model_str: nil)
         last_line = model_str[idx..].strip
       end
       if last_line.start_with?(pandas_key)
-        JSON.parse(last_line[pandas_key.length..])
+        pandas_categorical = JSON.parse(last_line[pandas_key.length..])
+        pandas_categorical.map { |cats| cats.each_with_index.to_h }
       end
     end
 

lib/lightgbm/inner_predictor.rb

@@ -140,7 +140,7 @@ def cached_feature_name
 
     def apply_pandas_categorical(data, categorical_feature, pandas_categorical)
       (categorical_feature || []).each_with_index do |cf, i|
-        cat_codes = pandas_categorical[i].map.with_index.to_h
+        cat_codes = pandas_categorical[i]
         data.each do |r|
           cat = r[cf]
           unless cat.nil?