title: Calculate the mode of a PySpark DataFrame column?
body: <p>Ultimately what I want is the mode of a column, for all the columns in the DataFrame.  For other summary statistics, I see a couple of options: use DataFrame aggregation, or map the columns of the DataFrame to an RDD of vectors (something I'm also having trouble doing) and use <code>colStats</code> from MLlib.  But I don't see mode as an option there.</p>