September 2017 Update

Task/Hash-join/Kotlin/hash-join.kotlin

@@ -0,0 +1,39 @@
+data class A(val age: Int, val name: String)
+
+data class B(val character: String, val nemesis: String)
+
+data class C(val rowA: A, val rowB: B)
+
+fun hashJoin(tableA: List<A>, tableB: List<B>): List<C> {
+    val mm = tableB.groupBy { it.character }
+    val tableC = mutableListOf<C>()
+    for (a in tableA) {
+        val value = mm[a.name] ?: continue
+        for (b in value) tableC.add(C(a, b))
+    }
+    return tableC.toList()
+}
+
+fun main(args: Array<String>) {
+    val tableA = listOf(
+        A(27, "Jonah"),
+        A(18, "Alan"),
+        A(28, "Glory"),
+        A(18, "Popeye"),
+        A(28, "Alan")
+    )
+    val tableB = listOf(
+        B("Jonah", "Whales"),
+        B("Jonah", "Spiders"),
+        B("Alan", "Ghosts"),
+        B("Alan", "Zombies"),
+        B("Glory", "Buffy")
+    )
+    val tableC = hashJoin(tableA, tableB)
+    println("A.Age A.Name B.Character B.Nemesis")
+    println("----- ------ ----------- ---------")
+    for (c in tableC) {
+        print("${c.rowA.age}    ${c.rowA.name.padEnd(6)} ")
+        println("${c.rowB.character.padEnd(6)}      ${c.rowB.nemesis}")
+    }
+}