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https://issues.apache.org/jira/browse/TAJO-921?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14386178#comment-14386178
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ASF GitHub Bot commented on TAJO-921:
-------------------------------------
Github user jihoonson commented on a diff in the pull request:
https://github.com/apache/tajo/pull/427#discussion_r27366305
--- Diff:
tajo-core/src/main/java/org/apache/tajo/engine/function/builtin/StdDev.java ---
@@ -0,0 +1,94 @@
+/**
+ * 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.tajo.engine.function.builtin;
+
+import org.apache.tajo.catalog.CatalogUtil;
+import org.apache.tajo.catalog.Column;
+import org.apache.tajo.common.TajoDataTypes.DataType;
+import org.apache.tajo.common.TajoDataTypes.Type;
+import org.apache.tajo.datum.Datum;
+import org.apache.tajo.datum.NullDatum;
+import org.apache.tajo.datum.ProtobufDatum;
+import org.apache.tajo.plan.function.AggFunction;
+import org.apache.tajo.plan.function.FunctionContext;
+import org.apache.tajo.storage.Tuple;
+
+import static org.apache.tajo.InternalTypes.StdDevProto;
+
+public abstract class StdDev extends AggFunction<Datum> {
+
+ public StdDev(Column[] definedArgs) {
+ super(definedArgs);
+ }
+
+ public StdDevContext newContext() {
+ return new StdDevContext();
+ }
+
+ @Override
+ public void eval(FunctionContext ctx, Tuple params) {
+ StdDevContext StdDevCtx = (StdDevContext) ctx;
+ Datum datum = params.get(0);
+ if (datum.isNotNull()) {
+ double delta = datum.asFloat8() - StdDevCtx.avg;
+ StdDevCtx.count++;
+ StdDevCtx.avg += delta/StdDevCtx.count;
+ StdDevCtx.squareSumOfDiff += delta * (datum.asFloat8() -
StdDevCtx.avg);
--- End diff --
```datum.asFloat8() - StdDevCtx.avg``` can be replaced with ```delta```.
> Add STDDEV_SAMP and STDDEV_POP window functions
> -----------------------------------------------
>
> Key: TAJO-921
> URL: https://issues.apache.org/jira/browse/TAJO-921
> Project: Tajo
> Issue Type: Sub-task
> Components: function/udf, physical operator
> Reporter: Hyunsik Choi
> Assignee: Keuntae Park
> Fix For: 0.11.0
>
>
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