[SPARK-7983] [MLLIB] Add require for one-based indices in loadLibSVMFile

jira: https://issues.apache.org/jira/browse/SPARK-7983

Customers frequently use zero-based indices in their LIBSVM files. No warnings or errors from Spark will be reported during their computation afterwards, and usually it will lead to wired result for many algorithms (like GBDT).

add a quick check.

Author: Yuhao Yang <hhbyyh@gmail.com>

Closes #6538 from hhbyyh/loadSVM and squashes the following commits:

79d9c11 [Yuhao Yang] optimization as respond to comments
4310710 [Yuhao Yang] merge conflict
96460f1 [Yuhao Yang] merge conflict
20a2811 [Yuhao Yang] use require
6e4f8ca [Yuhao Yang] add check for ascending order
9956365 [Yuhao Yang] add ut for 0-based loadlibsvm exception
5bd1f9a [Yuhao Yang] add require for one-based in loadLIBSVM

mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala

@@ -82,6 +82,18 @@ object MLUtils {
           val value = indexAndValue(1).toDouble
           (index, value)
         }.unzip
+
+        // check if indices are one-based and in ascending order
+        var previous = -1
+        var i = 0
+        val indicesLength = indices.length
+        while (i < indicesLength) {
+          val current = indices(i)
+          require(current > previous, "indices should be one-based and in ascending order" )
+          previous = current
+          i += 1
+        }
+
         (label, indices.toArray, values.toArray)
       }
 

mllib/src/test/scala/org/apache/spark/mllib/util/MLUtilsSuite.scala

@@ -25,6 +25,7 @@ import breeze.linalg.{squaredDistance => breezeSquaredDistance}
 import com.google.common.base.Charsets
 import com.google.common.io.Files
 
+import org.apache.spark.SparkException
 import org.apache.spark.SparkFunSuite
 import org.apache.spark.mllib.linalg.{DenseVector, SparseVector, Vectors}
 import org.apache.spark.mllib.regression.LabeledPoint
@@ -108,6 +109,40 @@ class MLUtilsSuite extends SparkFunSuite with MLlibTestSparkContext {
     Utils.deleteRecursively(tempDir)
   }
 
+  test("loadLibSVMFile throws IllegalArgumentException when indices is zero-based") {
+    val lines =
+      """
+        |0
+        |0 0:4.0 4:5.0 6:6.0
+      """.stripMargin
+    val tempDir = Utils.createTempDir()
+    val file = new File(tempDir.getPath, "part-00000")
+    Files.write(lines, file, Charsets.US_ASCII)
+    val path = tempDir.toURI.toString
+
+    intercept[SparkException] {
+      loadLibSVMFile(sc, path).collect()
+    }
+    Utils.deleteRecursively(tempDir)
+  }
+
+  test("loadLibSVMFile throws IllegalArgumentException when indices is not in ascending order") {
+    val lines =
+      """
+        |0
+        |0 3:4.0 2:5.0 6:6.0
+      """.stripMargin
+    val tempDir = Utils.createTempDir()
+    val file = new File(tempDir.getPath, "part-00000")
+    Files.write(lines, file, Charsets.US_ASCII)
+    val path = tempDir.toURI.toString
+
+    intercept[SparkException] {
+      loadLibSVMFile(sc, path).collect()
+    }
+    Utils.deleteRecursively(tempDir)
+  }
+
   test("saveAsLibSVMFile") {
     val examples = sc.parallelize(Seq(
       LabeledPoint(1.1, Vectors.sparse(3, Seq((0, 1.23), (2, 4.56)))),