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https://issues.apache.org/jira/browse/DRILL-556?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13984041#comment-13984041
]
ASF GitHub Bot commented on DRILL-556:
--------------------------------------
Github user amansinha100 commented on a diff in the pull request:
https://github.com/apache/incubator-drill/pull/56#discussion_r12080233
--- Diff: exec/java-exec/src/main/codegen/templates/AggrTypeFunctions3.java
---
@@ -0,0 +1,128 @@
+/**
+ * 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.
+ */
+<@pp.dropOutputFile />
+
+
+
+<#list aggrtypes2.aggrtypes as aggrtype>
+<#if aggrtype.className != "Avg">
+<@pp.changeOutputFile
name="/org/apache/drill/exec/expr/fn/impl/gaggr/${aggrtype.className}Functions.java"
/>
+
+<#include "/@includes/license.ftl" />
+
+<#-- A utility class that is used to generate java code for aggr functions
such as stddev, variance -->
+
+/*
+ * This class is automatically generated from AggrTypeFunctions2.tdd using
FreeMarker.
+ */
+
+package org.apache.drill.exec.expr.fn.impl.gaggr;
+
+import org.apache.drill.exec.expr.DrillAggFunc;
+import org.apache.drill.exec.expr.annotations.FunctionTemplate;
+import
org.apache.drill.exec.expr.annotations.FunctionTemplate.NullHandling;
+import
org.apache.drill.exec.expr.annotations.FunctionTemplate.FunctionScope;
+import org.apache.drill.exec.expr.annotations.Output;
+import org.apache.drill.exec.expr.annotations.Param;
+import org.apache.drill.exec.expr.annotations.Workspace;
+import org.apache.drill.exec.expr.holders.*;
+import org.apache.drill.exec.record.RecordBatch;
+
+@SuppressWarnings("unused")
+
+public class ${aggrtype.className}Functions {
+ static final org.slf4j.Logger logger =
org.slf4j.LoggerFactory.getLogger(${aggrtype.className}Functions.class);
+
+<#list aggrtype.types as type>
+
+<#if aggrtype.aliasName == "">
+@FunctionTemplate(name = "${aggrtype.funcName}", scope =
FunctionTemplate.FunctionScope.POINT_AGGREGATE)
+<#else>
+@FunctionTemplate(names = {"${aggrtype.funcName}",
"${aggrtype.aliasName}"}, scope =
FunctionTemplate.FunctionScope.POINT_AGGREGATE)
+</#if>
+
+public static class ${type.inputType}${aggrtype.className} implements
DrillAggFunc{
+
+ @Param ${type.inputType}Holder in;
+ @Workspace ${type.movingAverageType}Holder avg;
+ @Workspace ${type.movingDeviationType}Holder dev;
+ @Workspace ${type.countRunningType}Holder count;
+ @Output ${type.outputType}Holder out;
+
+ public void setup(RecordBatch b) {
+ avg = new ${type.movingAverageType}Holder();
+ dev = new ${type.movingDeviationType}Holder();
+ count = new ${type.countRunningType}Holder();
+
+ // Initialize the workspace variables
+ avg.value = 0;
+ dev.value = 0;
+ count.value = 1;
+ }
+
+ @Override
+ public void add() {
+ <#if type.inputType?starts_with("Nullable")>
+ sout: {
+ if (in.isSet == 0) {
+ // processing nullable input and the value is null, so don't do
anything...
+ break sout;
+ }
+ </#if>
+
+ // Welford's approach to compute standard deviation
--- End diff --
Welford's method does the computation online (streaming) and it looks
simple... so I am wondering is there a catch ? It is computing the
average each time a row is processed as opposed to doing it once at the end..so
we would have to see how it performs.
> Implement aggregate functions to compute standard deviation, variance
> ---------------------------------------------------------------------
>
> Key: DRILL-556
> URL: https://issues.apache.org/jira/browse/DRILL-556
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Mehant Baid
> Assignee: Mehant Baid
> Attachments: DRILL-556.patch
>
>
> Following are the aggregate functions to be added as part of this JIRA
> stddev()
> stddev_samp()
> stddev_pop()
> variance()
> var_samp()
> var_pop()
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