title: Why does dropna() not work?
body: <p>System: Spark 1.3.0 (Anaconda Python dist.) on Cloudera Quickstart VM 5.4</p>
  
  <p>Here's a Spark DataFrame:</p>
  
  <pre><code>from pyspark.sql import SQLContext
  from pyspark.sql.types import *
  sqlContext = SQLContext(sc)
  
  data = sc.parallelize([('Foo',41,'US',3),
                         ('Foo',39,'UK',1),
                         ('Bar',57,'CA',2),
                         ('Bar',72,'CA',3),
                         ('Baz',22,'US',6),
                         (None,75,None,7)])
  
  schema = StructType([StructField('Name', StringType(), True),
                       StructField('Age', IntegerType(), True),
                       StructField('Country', StringType(), True),
                       StructField('Score', IntegerType(), True)])
  
  df = sqlContext.createDataFrame(data,schema)
  </code></pre>
  
  <p><code>data.show()</code></p>
  
  <pre><code>Name Age Country Score
  Foo  41  US      3    
  Foo  39  UK      1    
  Bar  57  CA      2    
  Bar  72  CA      3    
  Baz  22  US      6    
  null 75  null    7 
  </code></pre>
  
  <p>However neither of these work!</p>
  
  <pre><code>df.dropna()
  df.na.drop()
  </code></pre>
  
  <p>I get this message:</p>
  
  <pre><code>&gt;&gt;&gt; df.show()
  Name Age Country Score
  Foo  41  US      3    
  Foo  39  UK      1    
  Bar  57  CA      2    
  Bar  72  CA      3    
  Baz  22  US      6    
  null 75  null    7    
  &gt;&gt;&gt; df.dropna().show()
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/usr/lib/spark/python/pyspark/sql/dataframe.py", line 580, in __getattr__
      jc = self._jdf.apply(name)
    File "/usr/lib/spark/python/lib/py4j-0.8.2.1-src.zip/py4j/java_gateway.py", line 538, in __call__
    File "/usr/lib/spark/python/lib/py4j-0.8.2.1-src.zip/py4j/protocol.py", line 300, in get_return_value
  py4j.protocol.Py4JJavaError: An error occurred while calling o50.apply.
  : org.apache.spark.sql.AnalysisException: Cannot resolve column name "dropna" among (Name, Age, Country, Score);
      at org.apache.spark.sql.DataFrame$$anonfun$resolve$1.apply(DataFrame.scala:162)
      at org.apache.spark.sql.DataFrame$$anonfun$resolve$1.apply(DataFrame.scala:162)
      at scala.Option.getOrElse(Option.scala:120)
      at org.apache.spark.sql.DataFrame.resolve(DataFrame.scala:161)
      at org.apache.spark.sql.DataFrame.col(DataFrame.scala:436)
      at org.apache.spark.sql.DataFrame.apply(DataFrame.scala:426)
      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 py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
      at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:379)
      at py4j.Gateway.invoke(Gateway.java:259)
      at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
      at py4j.commands.CallCommand.execute(CallCommand.java:79)
      at py4j.GatewayConnection.run(GatewayConnection.java:207)
      at java.lang.Thread.run(Thread.java:745)
  </code></pre>
  
  <p>Has anybody else experienced this problem? What's the workaround? Pyspark seems to thing that I am looking for a column called "na". Any help would be appreciated!</p>