Using the reduce and reduceByKey methods to calculate the results

In this section, we will use the reduce and reduceBykey functions to calculate our results and understand the behavior of reduce. We will then compare the reduce and reduceBykey functions to check which of the functions should be used in a particular use case.

We will first focus on the reduce API. First, we need to create an input of UserTransaction. We have the user transaction A with amount 10, B with amount 1, and A with amount 101. Let's say that we want to find out the global maximum. We are not interested in the data for the specific key, but in the global data. We want to scan it, take the maximum, and return it, as shown in the following example:

test("should use reduce API") {
    //given
    val input = spark.makeRDD(List(
    UserTransaction("A", 10),
    UserTransaction("B...