Support more value types in toDataFrame

Author: nikitinas

src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/toDataFrame.kt

@@ -30,7 +30,20 @@ import kotlin.reflect.full.memberProperties
 import kotlin.reflect.full.withNullability
 import kotlin.reflect.jvm.javaField
 
-internal val KClass<*>.isValueType: Boolean get() = this == String::class || this.isSubclassOf(Number::class) || this.isSubclassOf(Temporal::class)
+internal val valueTypes = setOf(
+    String::class,
+    Boolean::class,
+    kotlin.time.Duration::class,
+    kotlinx.datetime.LocalDate::class,
+    kotlinx.datetime.LocalDateTime::class,
+    kotlinx.datetime.Instant::class,
+)
+
+internal val KClass<*>.isValueType: Boolean get() =
+    this in valueTypes ||
+        this.isSubclassOf(Number::class) ||
+        this.isSubclassOf(Enum::class) ||
+        this.isSubclassOf(Temporal::class)
 
 internal class CreateDataFrameDslImpl<T>(
     override val source: Iterable<T>,

tests/src/test/kotlin/org/jetbrains/kotlinx/dataframe/api/toDataFrame.kt

@@ -104,4 +104,16 @@ class CreateDataFrameTests {
         df2.list.kind shouldBe ColumnKind.Frame
         df2.a.kind() shouldBe ColumnKind.Group
     }
+
+    enum class DummyEnum { A }
+
+    @Test
+    fun `don't convert value types`() {
+        data class Entry(val a: Int, val b: String, val c: Boolean, val e: DummyEnum)
+
+        val df = listOf(Entry(1, "s", true, DummyEnum.A)).toDataFrame(depth = 100)
+        df.columns().forEach {
+            it.kind shouldBe ColumnKind.Value
+        }
+    }
 }