[Documentation] fixed groupby aggregation example for pyspark

[mortada]

What changes were proposed in this pull request?

fixing documentation for the groupby/agg example in python

How was this patch tested?

the existing example in the documentation dose not contain valid syntax (missing parenthesis) and is not using Column in the expression for agg()

after the fix here's how I tested it:

In [1]: from pyspark.sql import Row

In [2]: import pyspark.sql.functions as func

In [3]: %cpaste
Pasting code; enter '--' alone on the line to stop or use Ctrl-D.
:records = [{'age': 19, 'department': 1, 'expense': 100},
: {'age': 20, 'department': 1, 'expense': 200},
: {'age': 21, 'department': 2, 'expense': 300},
: {'age': 22, 'department': 2, 'expense': 300},
: {'age': 23, 'department': 3, 'expense': 300}]
:--

In [4]: df = sqlContext.createDataFrame([Row(**d) for d in records])

In [5]: df.groupBy("department").agg(df["department"], func.max("age"), func.sum("expense")).show()

+----------+----------+--------+------------+
|department|department|max(age)|sum(expense)|
+----------+----------+--------+------------+
|         1|         1|      20|         300|
|         2|         2|      22|         600|
|         3|         3|      23|         300|
+----------+----------+--------+------------+

[AmplabJenkins]

Can one of the admins verify this patch?

[rxin]

Thanks - merging in master/2.0/1.6.