R is the latest language added to Apache Spark, and the SparkR API is slightly different from PySpark. With the release of Spark 2.0, the R API officially supports executing user code on distributed data. This is done through a family of apply() functions. In this talk I will give an overview of this new functionality in SparkR. Using this API requires some changes to regular code with dapply(). This talk will focus on how to correctly use this API to parallelize existing R packages. Most important topics of consideration will be performance and correctness when using the apply family of functions in SparkR.