Github user thvasilo commented on a diff in the pull request:
https://github.com/apache/flink/pull/861#discussion_r33148440
--- Diff:
flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/CategoricalHistogram.scala
---
@@ -0,0 +1,167 @@
+/*
+ * 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.math
+
+import java.util
+
+/** Implementation of a discrete valued online histogram
+ *
+ */
+class CategoricalHistogram(
+ values: Array[Double],
+ counts: Array[Int] = Array.ofDim[Int](0))
+ extends OnlineHistogram
+ with Serializable {
+
+ // sanity checks
+ require(values.length > 0, "Number of classes should be a positive
integer")
+ require(counts.length == 0 || counts.length == values.length, "Counts
should have the same " +
+ "number" + " " + "of " + "entries as values")
+ val data = new util.ArrayList[(Double, Int)](values.length)
+ require(checkSanity, "All values in counts should be non-negative")
+
+ /** Number of bins currently being used
+ *
+ * @return number of bins
+ */
+ override def bins: Int = {
+ data.size
+ }
+
+ /** Adds a new instance
+ *
+ * @param p value to be added
+ */
+ override def add(p: Double): Unit = {
+ // search for the index where the value is equal to1 p
+ val search = find(p)
+ require(search >= 0, p + "is not present in the histogram")
--- End diff --
Why is this a requirement? The point of an online histogram is the ability
to grow it incrementally.
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