Since ```Dataset``` has a new meaning in Spark 1.6, we should rename it to avoid confusion.
#9873 finished the work of Scala example, here we focus on the Python one.
Move dataset_example.py to ```examples/ml``` and rename to ```dataframe_example.py```.
BTW, fix minor missing issues of #9873.
cc mengxr

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #9957 from yanboliang/SPARK-11978.

This PR update PySpark to support Python 3 (tested with 3.4).

Known issue: unpickle array from Pyrolite is broken in Python 3, those tests are skipped.

TODO: ec2/spark-ec2.py is not fully tested with python3.

Author: Davies Liu <davies@databricks.com>
Author: twneale <twneale@gmail.com>
Author: Josh Rosen <joshrosen@databricks.com>

Closes #5173 from davies/python3 and squashes the following commits:

d7d6323 [Davies Liu] fix tests
6c52a98 [Davies Liu] fix mllib test
99e334f [Davies Liu] update timeout
b716610 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
cafd5ec [Davies Liu] adddress comments from @mengxr
bf225d7 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
179fc8d [Davies Liu] tuning flaky tests
8c8b957 [Davies Liu] fix ResourceWarning in Python 3
5c57c95 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
4006829 [Davies Liu] fix test
2fc0066 [Davies Liu] add python3 path
71535e9 [Davies Liu] fix xrange and divide
5a55ab4 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
125f12c [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
ed498c8 [Davies Liu] fix compatibility with python 3
820e649 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
e8ce8c9 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
ad7c374 [Davies Liu] fix mllib test and warning
ef1fc2f [Davies Liu] fix tests
4eee14a [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
20112ff [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
59bb492 [Davies Liu] fix tests
1da268c [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
ca0fdd3 [Davies Liu] fix code style
9563a15 [Davies Liu] add imap back for python 2
0b1ec04 [Davies Liu] make python examples work with Python 3
d2fd566 [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
a716d34 [Davies Liu] test with python 3.4
f1700e8 [Davies Liu] fix test in python3
671b1db [Davies Liu] fix test in python3
692ff47 [Davies Liu] fix flaky test
7b9699f [Davies Liu] invalidate import cache for Python 3.3+
9c58497 [Davies Liu] fix kill worker
309bfbf [Davies Liu] keep compatibility
5707476 [Davies Liu] cleanup, fix hash of string in 3.3+
8662d5b [Davies Liu] Merge branch 'master' of github.com:apache/spark into python3
f53e1f0 [Davies Liu] fix tests
70b6b73 [Davies Liu] compile ec2/spark_ec2.py in python 3
a39167e [Davies Liu] support customize class in __main__
814c77b [Davies Liu] run unittests with python 3
7f4476e [Davies Liu] mllib tests passed
d737924 [Davies Liu] pass ml tests
375ea17 [Davies Liu] SQL tests pass
6cc42a9 [Davies Liu] rename
431a8de [Davies Liu] streaming tests pass
78901a7 [Davies Liu] fix hash of serializer in Python 3
24b2f2e [Davies Liu] pass all RDD tests
35f48fe [Davies Liu] run future again
1eebac2 [Davies Liu] fix conflict in ec2/spark_ec2.py
6e3c21d [Davies Liu] make cloudpickle work with Python3
2fb2db3 [Josh Rosen] Guard more changes behind sys.version; still doesn't run
1aa5e8f [twneale] Turned out `pickle.DictionaryType is dict` == True, so swapped it out
7354371 [twneale] buffer --> memoryview  I'm not super sure if this a valid change, but the 2.7 docs recommend using memoryview over buffer where possible, so hoping it'll work.
b69ccdf [twneale] Uses the pure python pickle._Pickler instead of c-extension _pickle.Pickler. It appears pyspark 2.7 uses the pure python pickler as well, so this shouldn't degrade pickling performance (?).
f40d925 [twneale] xrange --> range
e104215 [twneale] Replaces 2.7 types.InstsanceType with 3.4 `object`....could be horribly wrong depending on how types.InstanceType is used elsewhere in the package--see http://bugs.python.org/issue8206
79de9d0 [twneale] Replaces python2.7 `file` with 3.4 _io.TextIOWrapper
2adb42d [Josh Rosen] Fix up some import differences between Python 2 and 3
854be27 [Josh Rosen] Run `futurize` on Python code:
7c5b4ce [Josh Rosen] Remove Python 3 check in shell.py.

Use `sqlContext` in PySpark shell, make it consistent with SQL programming guide. `sqlCtx` is also kept for compatibility.

Author: Davies Liu <davies@databricks.com>

Closes #5425 from davies/sqlCtx and squashes the following commits:

af67340 [Davies Liu] sqlCtx -> sqlContext
15a278f [Davies Liu] use sqlContext in python shell

This pull request redesigns the existing Spark SQL dsl, which already provides data frame like functionalities.

TODOs:
With the exception of Python support, other tasks can be done in separate, follow-up PRs.
- [ ] Audit of the API
- [ ] Documentation
- [ ] More test cases to cover the new API
- [x] Python support
- [ ] Type alias SchemaRDD

Author: Reynold Xin <rxin@databricks.com>
Author: Davies Liu <davies@databricks.com>

Closes #4173 from rxin/df1 and squashes the following commits:

0a1a73b [Reynold Xin] Merge branch 'df1' of github.com:rxin/spark into df1
23b4427 [Reynold Xin] Mima.
828f70d [Reynold Xin] Merge pull request #7 from davies/df
257b9e6 [Davies Liu] add repartition
6bf2b73 [Davies Liu] fix collect with UDT and tests
e971078 [Reynold Xin] Missing quotes.
b9306b4 [Reynold Xin] Remove removeColumn/updateColumn for now.
a728bf2 [Reynold Xin] Example rename.
e8aa3d3 [Reynold Xin] groupby -> groupBy.
9662c9e [Davies Liu] improve DataFrame Python API
4ae51ea [Davies Liu] python API for dataframe
1e5e454 [Reynold Xin] Fixed a bug with symbol conversion.
2ca74db [Reynold Xin] Couple minor fixes.
ea98ea1 [Reynold Xin] Documentation & literal expressions.
2b22684 [Reynold Xin] Got rid of IntelliJ problems.
02bbfbc [Reynold Xin] Tightening imports.
ffbce66 [Reynold Xin] Fixed compilation error.
59b6d8b [Reynold Xin] Style violation.
b85edfb [Reynold Xin] ALS.
8c37f0a [Reynold Xin] Made MLlib and examples compile
6d53134 [Reynold Xin] Hive module.
d35efd5 [Reynold Xin] Fixed compilation error.
ce4a5d2 [Reynold Xin] Fixed test cases in SQL except ParquetIOSuite.
66d5ef1 [Reynold Xin] SQLContext minor patch.
c9bcdc0 [Reynold Xin] Checkpoint: SQL module compiles!

Register MLlib's Vector as a SQL user-defined type (UDT) in both Scala and Python. With this PR, we can easily map a RDD[LabeledPoint] to a SchemaRDD, and then select columns or save to a Parquet file. Examples in Scala/Python are attached. The Scala code was copied from jkbradley.

~~This PR contains the changes from #3068 . I will rebase after #3068 is merged.~~

marmbrus jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #3070 from mengxr/SPARK-3573 and squashes the following commits:

3a0b6e5 [Xiangrui Meng] organize imports
236f0a0 [Xiangrui Meng] register vector as UDT and provide dataset examples