From 4d03729683a084162a7c8ca0de96ced85dae804b Mon Sep 17 00:00:00 2001
From: yepyao <yepyao@gmail.com>
Date: Fri, 16 May 2014 23:06:24 +0800
Subject: [PATCH] use ndcg@all in lambdarank for ndcg

---
 regrank/xgboost_regrank_obj.hpp | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/regrank/xgboost_regrank_obj.hpp b/regrank/xgboost_regrank_obj.hpp
index e0ef67f7a..5272b42fa 100644
--- a/regrank/xgboost_regrank_obj.hpp
+++ b/regrank/xgboost_regrank_obj.hpp
@@ -336,8 +336,15 @@ namespace xgboost{
         public:
             virtual ~LambdaRankObj_NDCG(void){}
 
-            inline float DCG(const std::vector<float> &labels){
-                return 1.0;
+            inline float CalcDCG( const std::vector<float> &labels ){
+                double sumdcg = 0.0;
+                for( size_t i = 0; i < labels.size(); i ++ ){
+                    const unsigned rel = labels[i];
+                    if( rel != 0 ){ 
+                        sumdcg += logf(2.0f) * ((1<<rel)-1) / logf( i + 2 );
+                    }
+                }
+                return static_cast<float>(sumdcg);
             }
 
             inline float GetIDCG(const std::vector<ListEntry> &sorted_list){
@@ -347,7 +354,7 @@ namespace xgboost{
                 }
 
                 std::sort(labels.begin(), labels.end(), std::greater<float>());
-                return DCG(labels);
+                return CalcDCG(labels);
             }
 
             /*