TODO

TODOS:
- Maybe the section for pulling data from sql databases whould be in another chapter;
- Add a chapter for date and datetime manipulation tools;
- Add a section to describe the new `withColumns()` method: https://spark.apache.org/docs/latest/api/python/reference/pyspark.sql/api/pyspark.sql.DataFrame.withColumns.html



LIST OF METHODS:



# Probably go to 2nd edition:
cache()
coalesce()
unpersist()
persist()

# Probably go to 2nd edition:
foreach()
foreachPartition()
replace()


# Probably go to 2nd edition:
sampleBy()
randomSplit()