Encapsulate fair regression params

src/LightGBM/Internal/CommandLineWrapper.hs

@@ -78,7 +78,6 @@ applicationPMap =
     [ (P.Regression P.L1, "regression_l1")
     , (P.Regression P.L2, "regression_l2")
     , (P.Regression P.Huber, "huber")
-    , (P.Regression P.Fair, "fair")
     , (P.Regression P.Poisson, "poisson")
     , (P.Regression P.Quantile, "quantile")
     , (P.Regression P.MAPE, "mape")
@@ -92,6 +91,9 @@ applicationPMap =
 mkTweedieString :: P.TweedieRegressionParam -> String
 mkTweedieString (P.TweedieVariancePower p) = "tweedie_variance_power=" ++ show p
 
+mkFairString :: P.FairRegressionParam -> String
+mkFairString (P.FairC pd) = "fair_c=" ++ show (unrefine pd)
+
 mkDartString :: P.DARTParam -> String
 mkDartString (P.DropRate r) = "drop_rate=" ++ show (unrefine r)
 mkDartString (P.SkipDrop r) = "skip_drop=" ++ show (unrefine r)
@@ -116,6 +118,8 @@ mkOptionString (P.Objective (P.MultiClass P.MultiClassOneVsAll n)) =
   ["application=multiclassova", "num_classes=" ++ show n]
 mkOptionString (P.Objective (P.Regression (P.Tweedie tparams))) =
   ["application=tweedie"] ++ map mkTweedieString tparams
+mkOptionString (P.Objective (P.Regression (P.Fair fparams))) =
+  ["application=fair"] ++ map mkFairString fparams
 mkOptionString (P.Objective a) = ["application=" ++ (applicationPMap M.! a)]
 mkOptionString (P.BoostingType (P.DART dartParams)) =
   ["boosting=dart"] ++ map mkDartString dartParams
@@ -205,7 +209,6 @@ mkOptionString (P.ValidInitScoreFile f) =
 mkOptionString (P.ForcedSplits f) = ["forced_splits=" ++ f]
 mkOptionString (P.Sigmoid d) = ["sigmoid=" ++ show (unrefine d)]
 mkOptionString (P.Alpha d) = ["alpha=" ++ show (unrefine d)]
-mkOptionString (P.FairC d) = ["fair_c=" ++ show (unrefine d)]
 mkOptionString (P.PoissonMaxDeltaStep d) =
   ["poisson_max_delta_step=" ++ show (unrefine d)]
 mkOptionString (P.ScalePosWeight d) = ["scale_pos_weight=" ++ show d]

src/LightGBM/Parameters.hs

@@ -18,6 +18,7 @@ module LightGBM.Parameters
   , DARTParam(..)
   , Device(..)
   , Direction(..)
+  , FairRegressionParam(..)
   , GOSSParam(..)
   , GPUParam(..)
   , LocalListenPort
@@ -119,7 +120,6 @@ data Param
   | ForcedSplits FilePath
   | Sigmoid PositiveDouble -- ^ Used in Binary classification and LambdaRank
   | Alpha OpenProperFraction -- ^ Used in Huber loss and Quantile regression
-  | FairC PositiveDouble -- ^ Used in Fair loss
   | PoissonMaxDeltaStep PositiveDouble -- ^ Used in Poisson regression
   | ScalePosWeight Double -- ^ Used in Binary classification
   | BoostFromAverage Bool -- ^ Used only in RegressionL2 task
@@ -132,6 +132,12 @@ data Param
   | TrainingMetric Bool
   deriving (Eq, Show)
 
+-- | Parameters for Fair loss regression
+data FairRegressionParam =
+  FairC PositiveDouble
+  deriving (Eq, Show, Generic)
+instance Hashable FairRegressionParam
+
 -- | Different types of Boosting approaches
 data Booster
   = GBDT -- ^ Gradient Boosting Decision Tree
@@ -151,7 +157,7 @@ data RegressionApp
   = L1 -- ^ Absolute error metric
   | L2 -- ^ RMS errror metric
   | Huber
-  | Fair
+  | Fair [FairRegressionParam]
   | Poisson
   | Quantile
   | MAPE