This patch contains three how-to related to datetime:

1)How to convert a datetime column to string and back again to datetime
2)How to convert a datetime column to unix timestamp
3)How to split datetime column into multiple column
Merge pull request #15 from papayawarrior/master

Add how-to for finding the top-k rows within a grouping variable.
Merge pull request #16 from papayawarrior/master

Add how-to for checking if one graph is a subgraph of another.
Add the subgraph check to the readme.
datetime how-to
Update convert_column_to_timestamp.py
Update convert_column_to_timestamp.py
Update split_datetime_column.py
Update README.md
Merge pull request #9 from graphlab-code/datetime-how-to

This patch contains three how-to related to datetime:
Organized the how-tos based on categories. Changed the yelp how-to
to a JSON how-to.
Merge pull request #17 from srikris/how-to-reorg

Organized the how-tos based on categories. Changed the yelp how-to a JSON how-to.
Added ingress how-tos for Pandas, SQL, and Spark.
Initial check-in of how-to for Avro ingestion
- added comment to show snippet of SFrame after column renaming
- updated README
Made small changes.
Merge pull request #18 from graphlab-code/avro_howto

Initial check-in of how-to for Avro ingestion
Merge branch 'master' into ingress-how-to

Conflicts:
	README.md
Merge pull request #19 from srikris/ingress-how-to

Added ingress how-tos for Pandas, SQL, and Spark.