Kotlin - Associate With While Filtering Null Values?

Question

I am looking to create Map<Integer, EmployeeReport> using the below lambda. Is there a clean way to do this in Kotlin? What I essentially need to do is an associateWith operation but filtering out all null values that would be returned.

employeeById.keys.associateWith {
     val employeeData = getEmployeeData()
     if(employeeData == null){ null }
     else { EmployeeReport(employeeData) }
}

I feel like I could accomplish what I am looking for with the below code, but I'm wondering if there is a cleaner way.

employeeById.keys.mapNotNull{
      val employeeData = getEmployeeData()
      if(employeeData.isNull()){ null }
      else { Pair(it, EmployeeReport(employeeData)) }
}.associate { it.first to it.second }

Thank you. Any advice is appreciated.

Answer 1

One option would be to use toMap() (as @Tenfour04 suggested) and simplify the if else, like below

employeeById.keys.mapNotNull { key ->
    getEmployeeData()?.let { key to EmployeeReport(it) }
}.toMap()

Another option would be to define a function similar to the associateWith funtion of Kotlin with Kotlin's buildMap (ref) builder function

inline fun <K, V> Iterable<K>.associateWithNotNull(
    valueTransform: (K) -> V?,
): Map<K, V> = buildMap {
    for (key in this@associateWithNotNull) {
        val value = valueTransform(key) ?: continue
        this[key] = value
    }
}

and then using it as

employeeById.keys.associateWithNotNull { key ->
    getEmployeeData()?.let { EmployeeReport(it) }
}