Github user skonto commented on a diff in the pull request:
https://github.com/apache/flink/pull/3192#discussion_r98456054
--- Diff:
flink-libraries/flink-ml/src/main/scala/org/apache/flink/ml/clustering/KMeans.scala
---
@@ -0,0 +1,263 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.clustering
+
+import
org.apache.flink.api.java.functions.FunctionAnnotation.ForwardedFields
+import org.apache.flink.api.scala.{DataSet, _}
+import org.apache.flink.ml._
+import org.apache.flink.ml.common.{LabeledVector, _}
+import org.apache.flink.ml.math.Breeze._
+import org.apache.flink.ml.math.{BLAS, Vector}
+import org.apache.flink.ml.metrics.distances.EuclideanDistanceMetric
+import org.apache.flink.ml.pipeline._
+
+
+/**
+ * Implements the KMeans algorithm which calculates cluster centroids
based on set of training data
+ * points and a set of k initial centroids.
+ *
+ * [[KMeans]] is a [[Predictor]] which needs to be trained on a set of
data points and can then be
+ * used to assign new points to the learned cluster centroids.
+ *
+ * The KMeans algorithm works as described on Wikipedia
+ * (http://en.wikipedia.org/wiki/K-means_clustering):
+ *
+ * Given an initial set of k means m1(1),â¦,mk(1) (see below), the
algorithm proceeds by alternating
+ * between two steps:
+ *
+ * ===Assignment step:===
+ *
+ * Assign each observation to the cluster whose mean yields the least
within-cluster sum of
+ * squares (WCSS). Since the sum of squares is the squared Euclidean
distance, this is intuitively
+ * the "nearest" mean. (Mathematically, this means partitioning the
observations according to the
+ * Voronoi diagram generated by the means).
+ *
+ * `S_i^(t) = { x_p : || x_p - m_i^(t) ||^2 ⤠|| x_p - m_j^(t) ||^2
\forall j, 1 ⤠j ⤠k}`,
+ * where each `x_p` is assigned to exactly one `S^{(t)}`, even if it
could be assigned to two or
+ * more of them.
+ *
+ * ===Update step:===
+ *
+ * Calculate the new means to be the centroids of the observations in the
new clusters.
+ *
+ * `m^{(t+1)}_i = ( 1 / |S^{(t)}_i| ) \sum_{x_j \in S^{(t)}_i} x_j`
+ *
+ * Since the arithmetic mean is a least-squares estimator, this also
minimizes the within-cluster
+ * sum of squares (WCSS) objective.
+ *
+ * @example
+ * {{{
+ * val trainingDS: DataSet[Vector] =
env.fromCollection(Clustering.trainingData)
+ * val initialCentroids: DataSet[LabledVector] =
env.fromCollection(Clustering.initCentroids)
+ *
+ * val kmeans = KMeans()
+ * .setInitialCentroids(initialCentroids)
+ * .setNumIterations(10)
+ *
+ * kmeans.fit(trainingDS)
--- End diff --
A sidenote. In general I am fine with pipelines API but in this case for
example `train` would be more appropriate as the method instead of fit.
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