title: How to calculate Median in spark sqlContext for column of data type double
body: <p>I have given the sample table. I want to get the median from "value" column for each group "source" column. Where
  source column is of String DataType
  value column is of double DataType</p>
  
  <pre><code>scala&gt; sqlContext.sql("SELECT * from tTab order by source").show
  
  +---------------+-----+                                                         
  |         Source|value|
  +---------------+-----+
  |131.183.222.110|  1.0|
  | 131.183.222.85|  1.0|
  | 131.183.222.85|  0.0|
  | 131.183.222.85|  0.5|
  | 131.183.222.85|  1.0|
  | 131.183.222.85|  1.0|
  |   43.230.146.7|  0.0|
  |   43.230.146.7|  1.0|
  |   43.230.146.7|  1.0|
  |   43.230.146.8|  1.0|
  |   43.230.146.8|  1.0| 
  +---------------+-----+
  
  scala&gt; tTab.printSchema
  
  root
   |-- Source: string (nullable = true)
   |-- value: double (nullable = true)
  </code></pre>
  
  <p>Expected Answer:</p>
  
  <pre><code>+---------------+-----+
  |         Source|value|
  +---------------+-----+
  |131.183.222.110|  1.0|
  | 131.183.222.85|  1.0|
  |   43.230.146.7|  1.0|
  |   43.230.146.8|  1.0|
  +---------------+-----+
  </code></pre>
  
  <p>If "value" column would have been Int, below query is working. Since "value" is of data type as double, it is giving me error:</p>
  
  <pre><code> sqlContext.sql("SELECT source , percentile(value,0.5) OVER (PARTITION BY source) AS Median from tTab ").show
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>org.apache.hadoop.hive.ql.exec.NoMatchingMethodException: No matching method for class org.apache.hadoop.hive.ql.udf.UDAFPercentile with (double, double). Possible choices: _FUNC_(bigint, array&lt;double&gt;)  _FUNC_(bigint, double)  
      at org.apache.hadoop.hive.ql.exec.FunctionRegistry.getMethodInternal(FunctionRegistry.java:1164)
      at org.apache.hadoop.hive.ql.exec.DefaultUDAFEvaluatorResolver.getEvaluatorClass(DefaultUDAFEvaluatorResolver.java:83)
      at org.apache.hadoop.hive.ql.udf.generic.GenericUDAFBridge.getEvaluator(GenericUDAFBridge.java:56)
      at org.apache.hadoop.hive.ql.udf.generic.AbstractGenericUDAFResolver.getEvaluator(AbstractGenericUDAFResolver.java:47)
      at org.apache.spark.sql.hive.HiveWindowFunction.evaluator$lzycompute(hiveUDFs.scala:351)
      at org.apache.spark.sql.hive.HiveWindowFunction.evaluator(hiveUDFs.scala:349)
      at org.apache.spark.sql.hive.HiveWindowFunction.returnInspector$lzycompute(hiveUDFs.scala:357)
      at org.apache.spark.sql.hive.HiveWindowFunction.returnInspector(hiveUDFs.scala:356)
      at org.apache.spark.sql.hive.HiveWindowFunction.dataType(hiveUDFs.scala:362)
      at org.apache.spark.sql.catalyst.expressions.WindowExpression.dataType(windowExpressions.scala:313)
      at org.apache.spark.sql.catalyst.expressions.Alias.toAttribute(namedExpressions.scala:140)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$$anonfun$35$$anonfun$apply$15.applyOrElse(Analyzer.scala:856)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$$anonfun$35$$anonfun$apply$15.applyOrElse(Analyzer.scala:852)
      at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$3.apply(TreeNode.scala:227)
      at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$3.apply(TreeNode.scala:227)
      at org.apache.spark.sql.catalyst.trees.CurrentOrigin$.withOrigin(TreeNode.scala:51)
      at org.apache.spark.sql.catalyst.trees.TreeNode.transformDown(TreeNode.scala:226)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$$anonfun$35.apply(Analyzer.scala:852)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$$anonfun$35.apply(Analyzer.scala:863)
      at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
      at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
      at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
      at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
      at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
      at scala.collection.AbstractTraversable.map(Traversable.scala:105)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$.org$apache$spark$sql$catalyst$analysis$Analyzer$ExtractWindowExpressions$$addWindow(Analyzer.scala:849)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$$anonfun$apply$16.applyOrElse(Analyzer.scala:957)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$$anonfun$apply$16.applyOrElse(Analyzer.scala:913)
      at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$3.apply(TreeNode.scala:227)
      at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$3.apply(TreeNode.scala:227)
      at org.apache.spark.sql.catalyst.trees.CurrentOrigin$.withOrigin(TreeNode.scala:51)
      at org.apache.spark.sql.catalyst.trees.TreeNode.transformDown(TreeNode.scala:226)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$.apply(Analyzer.scala:913)
      at org.apache.spark.sql.catalyst.analysis.Analyzer$ExtractWindowExpressions$.apply(Analyzer.scala:745)
      at org.apache.spark.sql.catalyst.rules.RuleExecutor$$anonfun$execute$1$$anonfun$apply$1.apply(RuleExecutor.scala:83)
      at org.apache.spark.sql.catalyst.rules.RuleExecutor$$anonfun$execute$1$$anonfun$apply$1.apply(RuleExecutor.scala:80)
      at scala.collection.LinearSeqOptimized$class.foldLeft(LinearSeqOptimized.scala:111)
      at scala.collection.immutable.List.foldLeft(List.scala:84)
      at org.apache.spark.sql.catalyst.rules.RuleExecutor$$anonfun$execute$1.apply(RuleExecutor.scala:80)
      at org.apache.spark.sql.catalyst.rules.RuleExecutor$$anonfun$execute$1.apply(RuleExecutor.scala:72)
      at scala.collection.immutable.List.foreach(List.scala:318)
      at org.apache.spark.sql.catalyst.rules.RuleExecutor.execute(RuleExecutor.scala:72)
      at org.apache.spark.sql.SQLContext$QueryExecution.analyzed$lzycompute(SQLContext.scala:916)
      at org.apache.spark.sql.SQLContext$QueryExecution.analyzed(SQLContext.scala:916)
      at org.apache.spark.sql.SQLContext$QueryExecution.assertAnalyzed(SQLContext.scala:914)
      at org.apache.spark.sql.DataFrame.&lt;init&gt;(DataFrame.scala:132)
      at org.apache.spark.sql.DataFrame$.apply(DataFrame.scala:51)
      at org.apache.spark.sql.SQLContext.sql(SQLContext.scala:725)
      at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.&lt;init&gt;(&lt;console&gt;:20)
      at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.&lt;init&gt;(&lt;console&gt;:25)
      at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC.&lt;init&gt;(&lt;console&gt;:27)
      at $iwC$$iwC$$iwC$$iwC$$iwC.&lt;init&gt;(&lt;console&gt;:29)
      at $iwC$$iwC$$iwC$$iwC.&lt;init&gt;(&lt;console&gt;:31)
      at $iwC$$iwC$$iwC.&lt;init&gt;(&lt;console&gt;:33)
      at $iwC$$iwC.&lt;init&gt;(&lt;console&gt;:35)
      at $iwC.&lt;init&gt;(&lt;console&gt;:37)
      at &lt;init&gt;(&lt;console&gt;:39)
      at .&lt;init&gt;(&lt;console&gt;:43)
      at .&lt;clinit&gt;(&lt;console&gt;)
      at .&lt;init&gt;(&lt;console&gt;:7)
      at .&lt;clinit&gt;(&lt;console&gt;)
      at $print(&lt;console&gt;)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:606)
      at org.apache.spark.repl.SparkIMain$ReadEvalPrint.call(SparkIMain.scala:1065)
      at org.apache.spark.repl.SparkIMain$Request.loadAndRun(SparkIMain.scala:1340)
      at org.apache.spark.repl.SparkIMain.loadAndRunReq$1(SparkIMain.scala:840)
      at org.apache.spark.repl.SparkIMain.interpret(SparkIMain.scala:871)
      at org.apache.spark.repl.SparkIMain.interpret(SparkIMain.scala:819)
      at org.apache.spark.repl.SparkILoop.reallyInterpret$1(SparkILoop.scala:857)
      at org.apache.spark.repl.SparkILoop.interpretStartingWith(SparkILoop.scala:902)
      at org.apache.spark.repl.SparkILoop.command(SparkILoop.scala:814)
      at org.apache.spark.repl.SparkILoop.processLine$1(SparkILoop.scala:657)
      at org.apache.spark.repl.SparkILoop.innerLoop$1(SparkILoop.scala:665)
      at org.apache.spark.repl.SparkILoop.org$apache$spark$repl$SparkILoop$$loop(SparkILoop.scala:670)
      at org.apache.spark.repl.SparkILoop$$anonfun$org$apache$spark$repl$SparkILoop$$process$1.apply$mcZ$sp(SparkILoop.scala:997)
      at org.apache.spark.repl.SparkILoop$$anonfun$org$apache$spark$repl$SparkILoop$$process$1.apply(SparkILoop.scala:945)
      at org.apache.spark.repl.SparkILoop$$anonfun$org$apache$spark$repl$SparkILoop$$process$1.apply(SparkILoop.scala:945)
      at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
      at org.apache.spark.repl.SparkILoop.org$apache$spark$repl$SparkILoop$$process(SparkILoop.scala:945)
      at org.apache.spark.repl.SparkILoop.process(SparkILoop.scala:1059)
      at org.apache.spark.repl.Main$.main(Main.scala:31)
      at org.apache.spark.repl.Main.main(Main.scala)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:606)
      at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:672)
      at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:180)
      at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:205)
      at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:120)
      at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
  </code></pre>
  
  <p>Thank you so much!</p>