average-groupingby-aggregate.kt

// prepare variable employees which is a list of Employee object
// Same as Task 0
var groupCount = 0
employees.groupingBy { it.department }
    .aggregate { key, kAverage: Double?, element, isFirstElement ->
        // Reset the group count
        if (isFirstElement) {
            groupCount = 1
        } else {
            groupCount++
        }
        return@aggregate if (isFirstElement) {
            0.0 + element.salary
        } else {
            kAverage!! + (element.salary - kAverage)/(groupCount + 1)
        }
    }
    .map {
        println("Average salary for department ${it.key} is ${it.value}")
    }