[SPARK-4409] Modified genRandMatrix

Author: brkyvz

mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala

@@ -19,7 +19,7 @@ package org.apache.spark.mllib.linalg
 
 import java.util.{Arrays, Random}
 
-import scala.collection.mutable.{ArrayBuffer, ArrayBuilder, Map}
+import scala.collection.mutable.{ArrayBuffer, ArrayBuilder, Map => MutableMap}
 
 import breeze.linalg.{CSCMatrix => BSM, DenseMatrix => BDM, Matrix => BM}
 
@@ -408,8 +408,15 @@ object SparseMatrix {
     require(density >= 0.0 && density <= 1.0, "density must be a double in the range " +
       s"0.0 <= d <= 1.0. Currently, density: $density")
     val length = math.ceil(numRows * numCols * density).toInt
-    val entries = Map[(Int, Int), Double]()
+    val entries = MutableMap[(Int, Int), Double]()
     var i = 0
+    if (density == 0.0) {
+      return new SparseMatrix(numRows, numCols, new Array[Int](numCols + 1),
+        Array[Int](), Array[Double]())
+    } else if (density == 1.0) {
+      return new SparseMatrix(numRows, numCols, (0 to numRows * numCols by numRows).toArray,
+        (0 until numRows * numCols).toArray, Array.fill(numRows * numCols)(method(rng)))
+    }
     // Expected number of iterations is less than 1.5 * length
     if (density < 0.34) {
       while (i < length) {
@@ -424,23 +431,18 @@ object SparseMatrix {
       }
     } else { // selection - rejection method
       var j = 0
-      val triesPerCol = math.ceil(length * 1.0 / numCols).toInt
       val pool = numRows * numCols
       // loop over columns so that the sort in fromCOO requires less sorting
       while (i < length && j < numCols) {
-        var k = 0
-        val leftFromPool = (numCols - j) * numRows
-        while (k < triesPerCol) {
-          if (rng.nextDouble() < 1.0 * (length - i) / (pool - leftFromPool)) {
-            var rowIndex = rng.nextInt(numRows)
-            val colIndex = j
-            while (entries.contains((rowIndex, colIndex))) {
-              rowIndex = rng.nextInt(numRows)
-            }
-            entries += (rowIndex, colIndex) -> method(rng)
+        var passedInPool = j * numRows
+        var r = 0
+        while (i < length && r < numRows) {
+          if (rng.nextDouble() < 1.0 * (length - i) / (pool - passedInPool)) {
+            entries += (r, j) -> method(rng)
             i += 1
           }
-          k += 1
+          r += 1
+          passedInPool += 1
         }
         j += 1
       }