Kotlin forEach, map, filter operations learned from https://developer.android.com/codelabs/basic-android-kotlin-training-collections

KotlinCollectionOperations.kt

fun main() {
    val peopleAges = mutableMapOf<String, Int>(
        "Fred" to 30,
        "Ann" to 23
    )
    peopleAges.put("Barbara", 42)
    peopleAges["Joe"] = 51
    peopleAges["Fred"] = 31
    peopleAges.forEach { print("${it.key} is ${it.value}, ") }
    println()
    println(peopleAges.map { "${it.key} is ${it.value}" }.joinToString(", ") )
    println()
    println(peopleAges)
    val filteredNames = peopleAges.filter { it.key.length < 4 }
	println(filteredNames)

}