[GitHub] [datasketches-java] AlexanderSaydakov commented on a diff in pull request #412: Changes to classic quantiles

[GitBox <gi...@apache.org>]

AlexanderSaydakov commented on code in PR #412:
URL: https://github.com/apache/datasketches-java/pull/412#discussion_r986069733


##########
src/main/java/org/apache/datasketches/quantiles/ItemsUnion.java:
##########
@@ -126,8 +137,8 @@ public void update(final ItemsSketch<T> sketchIn) {
    * @param srcMem Memory image of sketch to be merged
    * @param serDe an instance of ArrayOfItemsSerDe
    */
-  public void update(final Memory srcMem, final ArrayOfItemsSerDe<T> serDe) {
-    final ItemsSketch<T> that = ItemsSketch.getInstance(srcMem, comparator_, serDe);
+  public void union(final Memory srcMem, final ArrayOfItemsSerDe<T> serDe) { //TODO rename merge

Review Comment:
   no objections. I just saw this comment and thought that the time for breaking changes is now.



##########
src/main/java/org/apache/datasketches/QuantilesDoublesAPI.java:
##########
@@ -0,0 +1,325 @@
+/*
+ * 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.datasketches;
+
+import static org.apache.datasketches.QuantileSearchCriteria.INCLUSIVE;
+
+public interface QuantilesDoublesAPI extends QuantilesAPI {
+
+  /**
+   * Same as {@link #getCDF(double[], QuantileSearchCriteria) getCDF(splitPoints, INCLUSIVE)}
+   * @param splitPoints an array of <i>m</i> unique, monotonically increasing quantiles
+   * @return a CDF array of m+1 double ranks (or probabilities) on the interval [0.0, 1.0).
+   */
+  default double[] getCDF(double[] splitPoints) {
+    return getCDF(splitPoints, INCLUSIVE);
+  }
+
+  /**
+   * Returns an approximation to the Cumulative Distribution Function (CDF) of the input stream
+   * as a monotonically increasing array of double ranks (or probabilities) on the interval [0.0, 1.0],
+   * given a set of splitPoints.
+   * The last rank in the returned array is always 1.0.
+   *
+   * <p>The resulting approximations have a probabilistic guarantee that can be obtained from the
+   * getNormalizedRankError(false) function.
+   *
+   * <p>If the sketch is empty this returns null.</p>
+   *
+   * @param splitPoints an array of <i>m</i> unique, monotonically increasing quantiles
+   * that divide the real number line into <i>m+1</i> consecutive non-overlapping intervals.
+   * It is not necessary to include either the minimum or maximum quantiles
+   * of the input stream in these split points.
+   *
+   * <p>If searchCrit is INCLUSIVE, the definition of an "interval" is
+   * exclusive of the left splitPoint and
+   * inclusive of the right splitPoint.</p>
+   *
+   * <p>If searchCrit is EXCLUSIVE, the definition of an "interval" is
+   * inclusive of the left splitPoint and
+   * exclusive of the right splitPoint.</p>
+   *
+   *<p>The left "splitPoint" for the lowest interval is the
+   * lowest quantile from the input stream retained by the sketch.
+   * The right "splitPoint" for the highest interval is the
+   * highest quantile from the input stream retained by the sketch.
+   * </p>
+   *
+   * @param searchCrit if INCLUSIVE, the weight of a given splitPoint quantile,
+   * if it also exists as retained quantile by the sketch,
+   * is included into the interval below.
+   * Otherwise, it is included into the interval above.
+   *
+   * @return an CDF array of m+1 double ranks (or probabilities) on the interval [0.0, 1.0).
+   */
+  double[] getCDF(double[] splitPoints, QuantileSearchCriteria searchCrit);
+
+  /**
+   * Returns the maximum quantile of the stream. This is provided for convenience, but is distinct from the largest
+   * quantile retained by the sketch algorithm.
+   *
+   * <p>If the sketch is empty this returns NaN.</p>
+   *
+   * @return the maximum quantile of the stream
+   */
+  double getMaxQuantile();

Review Comment:
   I would say that "item" is fine generic term for input data of an arbitrary type. At least I find it less awkward than calling all input pieces of data "quantiles".



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