From 9f82b533664e139e31de7bbd0a0663ae88d9a1df Mon Sep 17 00:00:00 2001
From: tqchen <tianqi.tchen@gmail.com>
Date: Tue, 6 May 2014 16:50:46 -0700
Subject: [PATCH] add regrank utils

---
 regrank/xgboost_regrank_utils.h | 43 +++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 regrank/xgboost_regrank_utils.h

diff --git a/regrank/xgboost_regrank_utils.h b/regrank/xgboost_regrank_utils.h
new file mode 100644
index 000000000..580cedb81
--- /dev/null
+++ b/regrank/xgboost_regrank_utils.h
@@ -0,0 +1,43 @@
+#ifndef XGBOOST_REGRANK_UTILS_H
+#define XGBOOST_REGRANK_UTILS_H
+/*!
+ * \file xgboost_regrank_utils.h
+ * \brief useful helper functions
+ * \author Tianqi Chen, Kailong Chen
+ */
+namespace xgboost{
+    namespace regrank{
+        // simple helper function to do softmax
+        inline static void Softmax( std::vector<float>& rec ){
+            float wmax = rec[0];
+            for( size_t i = 1; i < rec.size(); ++ i ){
+                wmax = std::max( rec[i], wmax );
+            }
+            double wsum = 0.0f;
+            for( size_t i = 0; i < rec.size(); ++ i ){
+                rec[i] = expf(rec[i]-wmax);
+                    wsum += rec[i];
+            }
+            for( size_t i = 0; i < rec.size(); ++ i ){
+                rec[i] /= wsum;
+            }                
+        }        
+        // simple helper function to do softmax
+        inline static int FindMaxIndex( std::vector<float>& rec ){
+            size_t mxid = 0;
+            for( size_t i = 1; i < rec.size(); ++ i ){
+                if( rec[i] > rec[mxid] ) mxid = i;
+            }
+            return (int)mxid;
+        }        
+        inline static bool CmpFirst(const std::pair<float, unsigned> &a, const std::pair<float, unsigned> &b){
+            return a.first > b.first;
+        }
+        inline static bool CmpSecond(const std::pair<float, unsigned> &a, const std::pair<float, unsigned> &b){
+            return a.second > b.second;
+        }
+    };
+};
+
+#endif
+