Merge pull request #874 from sk1418/find-in-nested-list

[find-in-nested-list] find first element in list of list

Author: theangrydev

core-kotlin-modules/core-kotlin-collections-list-2/src/test/kotlin/findFirstMatchInNestedList/FindTheFirstMatchInNestedListUnitTest.kt

@@ -0,0 +1,91 @@
+package findFirstMatchInNestedList
+
+import org.junit.jupiter.api.Test
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+import kotlin.test.assertEquals
+
+data class Player(val name: String, val score: Int)
+
+data class Team(val name: String, val players: List<Player>)
+
+val teamA = Team(
+    "Team A", listOf(
+        Player("Sam", 7),
+        Player("Mike", 35),
+        Player("Vincent", 15),
+        Player("Paul", 12)
+    )
+)
+val teamB = Team(
+    "Team B", listOf(
+        Player("Tom", 50),
+        Player("Jim", 35),
+        Player("Kai", 150),
+        Player("Tim", 200)
+    )
+)
+val teamC = Team(
+    "Team C", listOf(
+        Player("Leo", 15),
+        Player("Sean", 25),
+        Player("Jack", 10),
+        Player("Tim", 8)
+    )
+)
+val teamD = Team(
+    "Team D", listOf(
+        Player("Eric", 54),
+        Player("Liam", 104),
+        Player("Kevin", 70),
+        Player("Peter", 177),
+    )
+)
+val teams = listOf(teamA, teamB, teamC, teamD)
+
+class FindTheFirstMatchInNestedListUnitTest {
+    private val log: Logger = LoggerFactory.getLogger(FindTheFirstMatchInNestedListUnitTest::class.java)
+
+    @Test
+    fun `when using flatmap and first then get the expected result`() {
+        val result = teams.flatMap { it.players }.first { it.score > 100 }
+        assertEquals(Player("Kai", 150), result)
+
+        teams.flatMap {
+            log.info("Transforming players of the team: ${it.name}")
+            it.players
+        }.first {
+            log.info("Checking the player: ${it.name}")
+            it.score > 100
+        }
+    }
+
+    @Test
+    fun `when finding the first match using foreach then get the expected result`() {
+        fun findTheFirstPlayerHigherThan100(teams: List<Team>): Player {
+            teams.forEach { team ->
+                log.info("Checking players of the team: ${team.name}")
+                team.players.forEach { player ->
+                    log.info("|- Checking the player: ${player.name}")
+                    if (player.score > 100) return player
+                }
+            }
+            throw IllegalStateException("No matched player found")
+        }
+
+        val result = findTheFirstPlayerHigherThan100(teams)
+        assertEquals(Player("Kai", 150), result)
+    }
+
+    @Test
+    fun `when using sequence and then flatmap and first then get the expected result`() {
+        val result = teams.asSequence().flatMap {
+            log.info("Transforming players of the team: ${it.name}")
+            it.players
+        }.first {
+            log.info("|- Checking the player: ${it.name}")
+            it.score > 100
+        }
+        assertEquals(Player("Kai", 150), result)
+    }
+}