Merge pull request #128 from metarank/fix/libsvm-feature-index

libsvm format assumes feature index numbering from 1

Author: shuttie

src/main/scala/io/github/metarank/ltrlib/booster/CatboostBooster.scala

@@ -51,7 +51,7 @@ object CatboostBooster extends BoosterFactory[String, CatboostBooster, CatboostO
   override def formatData(ds: BoosterDataset, parent: Option[String]): String = {
     val file   = File.newTemporaryFile("catboost-", ".svm")
     val stream = file.newFileOutputStream()
-    LibSVMOutputFormat.write(stream, ds.original, 1)
+    LibSVMOutputFormat.write(stream, ds.original)
     stream.close()
     s"libsvm://$file"
   }

src/main/scala/io/github/metarank/ltrlib/output/LibSVMOutputFormat.scala

@@ -5,12 +5,12 @@ import io.github.metarank.ltrlib.model.Dataset
 import java.io.OutputStream
 
 object LibSVMOutputFormat extends OutputFormat {
-  def write(data: OutputStream, ds: Dataset, offset: Int = 0) = {
+  def write(data: OutputStream, ds: Dataset) = {
     for {
       query <- ds.groups
       rowid <- 0 until query.rows
     } {
-      val features = query.getRow(rowid).zipWithIndex.filter(_._1 != 0).map(x => s"${x._2 + offset}:${x._1}")
+      val features = query.getRow(rowid).zipWithIndex.filter(_._1 != 0).map(x => s"${x._2 + 1}:${x._1}")
       val label    = math.round(query.labels(rowid)).toString
       val line     = (List(label, s"qid:${query.group}") ++ features).mkString("", " ", "\n")
       data.write(line.getBytes())
@@ -25,7 +25,7 @@ object LibSVMOutputFormat extends OutputFormat {
       for {
         rowid <- 0 until query.rows
       } {
-        val features = query.getRow(rowid).zipWithIndex.filter(_._1 != 0).map(x => s"${x._2}:${x._1}").toList
+        val features = query.getRow(rowid).zipWithIndex.filter(_._1 != 0).map(x => s"${x._2 + 1}:${x._1}").toList
         val label    = math.round(query.labels(rowid)).toString
         val line     = (List(label) ++ features).mkString("", " ", "\n")
         data.write(line.getBytes())

src/test/scala/io/github/metarank/ltrlib/output/LibSVMOutputFormatTest.scala

@@ -23,9 +23,9 @@ class LibSVMOutputFormatTest extends AnyFlatSpec with Matchers {
     LibSVMOutputFormat.write(out, ds)
     val str = new String(out.toByteArray)
     str shouldBe
-      """1 qid:1 0:1.0 1:2.0
+      """1 qid:1 1:1.0 2:2.0
         |0 qid:1
-        |1 qid:2 0:1.0 1:NaN
+        |1 qid:2 1:1.0 2:NaN
         |""".stripMargin
   }
 
@@ -36,9 +36,9 @@ class LibSVMOutputFormatTest extends AnyFlatSpec with Matchers {
     val str  = new String(data.toByteArray)
     val gstr = new String(groups.toByteArray)
     str shouldBe
-      """1 0:1.0 1:2.0
+      """1 1:1.0 2:2.0
         |0
-        |1 0:1.0 1:NaN
+        |1 1:1.0 2:NaN
         |""".stripMargin
     gstr shouldBe "2\n1\n"
   }