Github user cestella commented on a diff in the pull request:
https://github.com/apache/incubator-metron/pull/226#discussion_r76100309
--- Diff:
metron-platform/metron-common/src/main/java/org/apache/metron/common/dsl/functions/StellarStatistics.java
---
@@ -0,0 +1,207 @@
+/*
+ *
+ * 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.metron.common.dsl.functions;
+
+import org.apache.commons.lang.NotImplementedException;
+import org.apache.commons.math3.stat.descriptive.DescriptiveStatistics;
+import org.apache.commons.math3.stat.descriptive.SummaryStatistics;
+
+import java.io.Serializable;
+
+/**
+ * Provides basic summary statistics to Stellar.
+ *
+ * Used as an adapter to provide a single interface to two underlying
Commons
+ * Math classes that provide summary statistics.
+ */
+public class StellarStatistics implements Serializable {
+
+ /**
+ * DescriptiveStatistics stores a rolling window of input data elements
+ * which is then used to calculate the summary statistic. There are some
+ * summary statistics like kurtosis and percentiles, that can only
+ * be calculated with this.
+ *
+ * This implementation is used if the windowSize > 0.
+ */
+ private DescriptiveStatistics descStats;
+
+ /**
+ * SummaryStatistics can be used for summary statistics that only
+ * require a single pass over the input data. This has the advantage
+ * of being less memory intensive, but not all summary statistics are
+ * available.
+ *
+ * This implementation is used if the windowSize == 0.
+ */
+ private SummaryStatistics summStats;
+
+ /**
+ * @param windowSize The number of input data elements to maintain in
memory. If
+ * windowSize == 0, then no data elements will be
maintained in
+ * memory.
+ */
+ public StellarStatistics(int windowSize) {
--- End diff --
Can we move the functions for StellarStatistics into their own interface
and have two implementations, one backed by SummaryStatistics and one backed by
DescriptiveStatistics? We will likely have a third implementation,
ProbabalisticStatistics that supports approximate distributional stats while
not requiring a window size and I'd like it to be as simple as implementing an
interface, not adding to a branch at every method.
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