References¶

https://stackoverflow.com/questions/42171499/get-current-number-of-partitions-of-a-dataframe

coalesce vs repartition¶

https://hackernoon.com/managing-spark-partitions-with-coalesce-and-repartition-4050c57ad5c4m

Tips and Traps¶

1. You can use the split function to split a delimited string into an array. It is suggested that removing trailing separators before you apply the split function. Please refer to the split section before for more detailed discussions.

2. Some string functions (e.g., right, etc.) are available in the Spark SQL APIs but not available as Spark DataFrame APIs.

Tips and Traps¶

1. Watch out for NaNs ..., behave might not what you expect ...

2. None can be used for otherwise and yield null in DataFrame.

Column alias and postional columns can be used in group by in Spark SQL!!!

Notice the function when behaves like if-else.

https://spark.apache.org/docs/latest/api/java/org/apache/spark/sql/DataFrameStatFunctions.html

https://spark.apache.org/docs/latest/api/java/org/apache/spark/sql/DataFrameStatFunctions.html#approxQuantile-java.lang.String:A-double:A-double-

https://spark.apache.org/docs/latest/api/sql/index.html#approx_percentile