Github user cestella commented on a diff in the pull request:
https://github.com/apache/incubator-metron/pull/225#discussion_r75933341
--- Diff:
metron-platform/metron-common/src/main/java/org/apache/metron/common/dsl/functions/SummaryStatisticsFunctions.java
---
@@ -0,0 +1,198 @@
+/*
+ *
+ * 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.math3.stat.descriptive.SummaryStatistics;
+import org.apache.metron.common.dsl.BaseStellarFunction;
+
+import java.util.List;
+
+import static org.apache.metron.common.utils.ConversionUtils.convert;
+
+/**
+ * Provides Stellar functions that can calculate summary statistics on
+ * streams of data.
+ *
+ * These functions are limited to those that can be calculated in a
+ * single-pass so that the values are not stored in memory. This leverages
+ * the commons-math SummaryStatistics class.
+ */
+public class SummaryStatisticsFunctions {
+
+ /**
+ * Initialize the summary statistics.
+ *
+ * STATS_INIT ()
+ */
+ public static class Init extends BaseStellarFunction {
+ @Override
+ public Object apply(List<Object> args) {
+ return new SummaryStatistics();
+ }
+ }
+
+ /**
+ * Add an input value to those that are used to calculate the summary
statistics.
+ *
+ * STATS_ADD (value, stats)
+ */
+ public static class Add extends BaseStellarFunction {
+ @Override
+ public Object apply(List<Object> args) {
+ double value = convert(args.get(0), Double.class);
+ SummaryStatistics stats = convert(args.get(1),
SummaryStatistics.class);
+ stats.addValue(value);
+ return null;
--- End diff --
Should we return the SummaryStatistics class here? That way we can chain
them?
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