[SPARK-19319][BACKPORT-2.1][SPARKR] SparkR Kmeans summary returns err…

…or when the cluster size doesn't equal to k

## What changes were proposed in this pull request?

Backport fix of #16666

## How was this patch tested?

Backport unit tests

Author: [email protected] <[email protected]>

Closes #16761 from wangmiao1981/kmeansport.

R/pkg/R/mllib.R

@@ -599,6 +599,10 @@ setMethod("summary", signature(object = "IsotonicRegressionModel"),
 #' @param k number of centers.
 #' @param maxIter maximum iteration number.
 #' @param initMode the initialization algorithm choosen to fit the model.
+#' @param seed the random seed for cluster initialization
+#' @param initSteps the number of steps for the k-means|| initialization mode.
+#'                  This is an advanced setting, the default of 2 is almost always enough. Must be > 0.
+#' @param tol convergence tolerance of iterations.
 #' @param ... additional argument(s) passed to the method.
 #' @return \code{spark.kmeans} returns a fitted k-means model.
 #' @rdname spark.kmeans
@@ -628,11 +632,16 @@ setMethod("summary", signature(object = "IsotonicRegressionModel"),
 #' @note spark.kmeans since 2.0.0
 #' @seealso \link{predict}, \link{read.ml}, \link{write.ml}
 setMethod("spark.kmeans", signature(data = "SparkDataFrame", formula = "formula"),
-          function(data, formula, k = 2, maxIter = 20, initMode = c("k-means||", "random")) {
+          function(data, formula, k = 2, maxIter = 20, initMode = c("k-means||", "random"),
+                   seed = NULL, initSteps = 2, tol = 1E-4) {
             formula <- paste(deparse(formula), collapse = "")
             initMode <- match.arg(initMode)
+            if (!is.null(seed)) {
+              seed <- as.character(as.integer(seed))
+            }
             jobj <- callJStatic("org.apache.spark.ml.r.KMeansWrapper", "fit", data@sdf, formula,
-                                as.integer(k), as.integer(maxIter), initMode)
+                                as.integer(k), as.integer(maxIter), initMode, seed,
+                                as.integer(initSteps), as.numeric(tol))
             new("KMeansModel", jobj = jobj)
           })
 
@@ -671,10 +680,13 @@ setMethod("fitted", signature(object = "KMeansModel"),
 
 #' @param object a fitted k-means model.
 #' @return \code{summary} returns summary information of the fitted model, which is a list.
-#'         The list includes the model's \code{k} (number of cluster centers),
+#'         The list includes the model's \code{k} (the configured number of cluster centers),
 #'         \code{coefficients} (model cluster centers),
-#'         \code{size} (number of data points in each cluster), and \code{cluster}
-#'         (cluster centers of the transformed data).
+#'         \code{size} (number of data points in each cluster), \code{cluster}
+#'         (cluster centers of the transformed data), {is.loaded} (whether the model is loaded
+#'         from a saved file), and \code{clusterSize}
+#'         (the actual number of cluster centers. When using initMode = "random",
+#'         \code{clusterSize} may not equal to \code{k}).
 #' @rdname spark.kmeans
 #' @export
 #' @note summary(KMeansModel) since 2.0.0
@@ -686,16 +698,17 @@ setMethod("summary", signature(object = "KMeansModel"),
             coefficients <- callJMethod(jobj, "coefficients")
             k <- callJMethod(jobj, "k")
             size <- callJMethod(jobj, "size")
-            coefficients <- t(matrix(coefficients, ncol = k))
+            clusterSize <- callJMethod(jobj, "clusterSize")
+            coefficients <- t(matrix(coefficients, ncol = clusterSize))
             colnames(coefficients) <- unlist(features)
-            rownames(coefficients) <- 1:k
+            rownames(coefficients) <- 1:clusterSize
             cluster <- if (is.loaded) {
               NULL
             } else {
               dataFrame(callJMethod(jobj, "cluster"))
             }
             list(k = k, coefficients = coefficients, size = size,
-                 cluster = cluster, is.loaded = is.loaded)
+                 cluster = cluster, is.loaded = is.loaded, clusterSize = clusterSize)
           })
 
 #  Predicted values based on a k-means model

R/pkg/inst/tests/testthat/test_mllib.R

@@ -375,6 +375,33 @@ test_that("spark.kmeans", {
   expect_true(summary2$is.loaded)
 
   unlink(modelPath)
+
+  # Test Kmeans on dataset that is sensitive to seed value
+  col1 <- c(1, 2, 3, 4, 0, 1, 2, 3, 4, 0)
+  col2 <- c(1, 2, 3, 4, 0, 1, 2, 3, 4, 0)
+  col3 <- c(1, 2, 3, 4, 0, 1, 2, 3, 4, 0)
+  cols <- as.data.frame(cbind(col1, col2, col3))
+  df <- createDataFrame(cols)
+
+  model1 <- spark.kmeans(data = df, ~ ., k = 5, maxIter = 10,
+                         initMode = "random", seed = 1, tol = 1E-5)
+  model2 <- spark.kmeans(data = df, ~ ., k = 5, maxIter = 10,
+                         initMode = "random", seed = 22222, tol = 1E-5)
+
+  summary.model1 <- summary(model1)
+  summary.model2 <- summary(model2)
+  cluster1 <- summary.model1$cluster
+  cluster2 <- summary.model2$cluster
+  clusterSize1 <- summary.model1$clusterSize
+  clusterSize2 <- summary.model2$clusterSize
+
+  # The predicted clusters are different
+  expect_equal(sort(collect(distinct(select(cluster1, "prediction")))$prediction),
+               c(0, 1, 2, 3))
+  expect_equal(sort(collect(distinct(select(cluster2, "prediction")))$prediction),
+               c(0, 1, 2))
+  expect_equal(clusterSize1, 4)
+  expect_equal(clusterSize2, 3)
 })
 
 test_that("spark.mlp", {

mllib/src/main/scala/org/apache/spark/ml/r/KMeansWrapper.scala

@@ -43,6 +43,8 @@ private[r] class KMeansWrapper private (
 
   lazy val cluster: DataFrame = kMeansModel.summary.cluster
 
+  lazy val clusterSize: Int = kMeansModel.clusterCenters.size
+
   def fitted(method: String): DataFrame = {
     if (method == "centers") {
       kMeansModel.summary.predictions.drop(kMeansModel.getFeaturesCol)
@@ -68,7 +70,10 @@ private[r] object KMeansWrapper extends MLReadable[KMeansWrapper] {
       formula: String,
       k: Int,
       maxIter: Int,
-      initMode: String): KMeansWrapper = {
+      initMode: String,
+      seed: String,
+      initSteps: Int,
+      tol: Double): KMeansWrapper = {
 
     val rFormula = new RFormula()
       .setFormula(formula)
@@ -87,6 +92,10 @@ private[r] object KMeansWrapper extends MLReadable[KMeansWrapper] {
       .setMaxIter(maxIter)
       .setInitMode(initMode)
       .setFeaturesCol(rFormula.getFeaturesCol)
+      .setInitSteps(initSteps)
+      .setTol(tol)
+
+    if (seed != null && seed.length > 0) kMeans.setSeed(seed.toInt)
 
     val pipeline = new Pipeline()
       .setStages(Array(rFormulaModel, kMeans))