Hello,

I am getting an exception from catalyst when array types are used in the
return schema of gapply() function. 

Following is a (made-up) example:

------------------------------------------------------------
iris$flag = base::sample(1:2, nrow(iris), T, prob = c(0.5,0.5))
irisdf = createDataFrame(iris)

foo = function(key, x) {
  nr = nrow(x)
  nc = ncol(x)
  arr = c(  paste("rows=", nr), paste("cols=",nc) )
  data.frame(key, strings = arr, stringsAsFactors = F)
}

outSchema = structType(  structField('key', 'integer'),
                         structField('strings', 'array<string>')  )
result = SparkR::gapply(irisdf, "flag", foo, outSchema)
d = SparkR::collect(result)
------------------------------------------------------------

This code throws up the following error:

java.lang.RuntimeException: java.lang.String is not a valid external type
for schema of array<string>
        at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIterator.processNext(Unknown
Source)
        at
org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
        at
org.apache.spark.sql.execution.WholeStageCodegenExec$$anonfun$8$$anon$1.hasNext(WholeStageCodegenExec.scala:370)
        at
org.apache.spark.sql.execution.SparkPlan$$anonfun$4.apply(SparkPlan.scala:246)
        at
org.apache.spark.sql.execution.SparkPlan$$anonfun$4.apply(SparkPlan.scala:240)
        at
org.apache.spark.rdd.RDD$$anonfun$mapPartitionsInternal$1$$anonfun$apply$24.apply(RDD.scala:803)
        at
org.apache.spark.rdd.RDD$$anonfun$mapPartitionsInternal$1$$anonfun$apply$24.apply(RDD.scala:803)
        at 
org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38)
        at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:319)
        at org.apache.spark.rdd.RDD.iterator(RDD.scala:283)
        at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:70)
        at org.apache.spark.scheduler.Task.run(Task.scala:86)
        at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:274)
        at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)

Any thoughts?

Thank you,
Shirish



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