title: pyspark Column is not iterable
body: <p>Having this dataframe I am getting Column is not iterable when I try to groupBy and getting max: </p>
  
  <pre><code>linesWithSparkDF
  +---+-----+
  | id|cycle|
  +---+-----+
  | 31|   26|
  | 31|   28|
  | 31|   29|
  | 31|   97|
  | 31|   98|
  | 31|  100|
  | 31|  101|
  | 31|  111|
  | 31|  112|
  | 31|  113|
  +---+-----+
  only showing top 10 rows
  
  
  ipython-input-41-373452512490&gt; in runlgmodel2(model, data)
       65     linesWithSparkDF.show(10)
       66 
  ---&gt; 67     linesWithSparkGDF = linesWithSparkDF.groupBy(col("id")).agg(max(col("cycle")))
       68     print "linesWithSparkGDF"
       69 
  
  /usr/hdp/current/spark-client/python/pyspark/sql/column.py in __iter__(self)
      241 
      242     def __iter__(self):
  --&gt; 243         raise TypeError("Column is not iterable")
      244 
      245     # string methods
  
  TypeError: Column is not iterable
  </code></pre>