From: Tzu-Ming Kuo <b99902073@patty.(none)>
Date: Mon, 1 Jul 2013 15:57:43 +0000 (+0800)
Subject: Modify function group_classes in linear.cpp to ensure label[0] = 1 if class labels... 
X-Git-Tag: v194~10
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=a932c3fe99fe03a69197dcd0c89df1e6fa86cc24;p=liblinear

Modify function group_classes in linear.cpp to ensure label[0] = 1 if class labels are +1 and -1
---

diff --git a/linear.cpp b/linear.cpp
index 6fade58..77237dd 100644
--- a/linear.cpp
+++ b/linear.cpp
@@ -2140,6 +2140,24 @@ static void group_classes(const problem *prob, int *nr_class_ret, int **label_re
 		}
 	}
 
+	//
+	// Labels are ordered by their first occurrence in the training set. 
+	// However, for two-class sets with -1/+1 labels and -1 appears first, 
+	// we swap labels to ensure that internally the binary SVM has positive data corresponding to the +1 instances.
+	//
+	if (nr_class == 2 && label[0] == -1 && label[1] == 1)
+	{
+		swap(label[0],label[1]);
+		swap(count[0],count[1]);
+		for(i=0;i<l;i++)
+		{
+			if(data_label[i] == 0)
+				data_label[i] = 1;
+			else
+				data_label[i] = 0;
+		}
+	}
+
 	int *start = Malloc(int,nr_class);
 	start[0] = 0;
 	for(i=1;i<nr_class;i++)