CODEWITHSUNDEEP
pythonapache-sparkpyspark
AmirHd
AmirHd

Reputation: 10308

How to use dataframes within a map function in Spark?

Definitions:

I have a mapping function as follows:

def mappingFunction(element):
    # The dataframe lookup!
    lookupResult = sampleDF.filter(sampleDF[0] == element).collect()
    if len(lookupResult) > 0:
        print lookupResult
        return 1
    return 0

The problem:

Accessing sampleDF outside of the mapping function works perfectly fine but as soon as I use it inside the function I get the following error:

py4j.Py4JException: Method __getnewargs__([]) does not exist
    at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:335)
    at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:344)
    at py4j.Gateway.invoke(Gateway.java:252)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:209)
    at java.lang.Thread.run(Thread.java:744)

What else I tried:

I did try saving a temporary table and using the sqlContext select inside the map function and still couldn't get this to work. This is the error I get:

  File "/usr/lib64/python2.6/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib64/python2.6/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/usr/lib64/python2.6/pickle.py", line 686, in _batch_setitems
    save(v)
  File "/usr/lib64/python2.6/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/opt/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/usr/lib64/python2.6/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib64/python2.6/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/usr/lib64/python2.6/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/usr/lib64/python2.6/pickle.py", line 306, in save
    rv = reduce(self.proto)
TypeError: 'JavaPackage' object is not callable

What I am asking for:

I have tried to simplify my problem through simple example. Any help on how to use a dataframe inside a map function is highly appreciated.

Upvotes: 6

Views: 7052

Answers (1)

zero323
zero323

Reputation: 330413

It is not possible. Spark doesn't support nested operations on distributed data structures (RDDs, DataFrames, Datasets). Even if it did executing large number of jobs wouldn't be a good idea. Given the code you've shown you probably want to convert your RDD to a DataFrame and perform join wit

(rdd.map(x => (x, )).toDF(["element"])
  .join(sampleDF, sampleDF[0] == df[0])
  .groupBy("element")
  .agg(count("element") > 0))

On a side note printing inside map is completely useless not mention it add additional IO overhead.

Upvotes: 3

Related Questions