added tests and fixed NaN behavior for min/max functions

Author: Jolanrensen

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/DataColumnType.kt

@@ -7,6 +7,7 @@ import org.jetbrains.kotlinx.dataframe.columns.ColumnGroup
 import org.jetbrains.kotlinx.dataframe.columns.ColumnKind
 import org.jetbrains.kotlinx.dataframe.columns.FrameColumn
 import org.jetbrains.kotlinx.dataframe.columns.ValueColumn
+import org.jetbrains.kotlinx.dataframe.impl.isIntraComparable
 import org.jetbrains.kotlinx.dataframe.impl.isMixedNumber
 import org.jetbrains.kotlinx.dataframe.impl.isPrimitiveNumber
 import org.jetbrains.kotlinx.dataframe.impl.isPrimitiveOrMixedNumber
@@ -18,11 +19,7 @@ import org.jetbrains.kotlinx.dataframe.util.IS_INTER_COMPARABLE_IMPORT
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 import kotlin.reflect.KType
-import kotlin.reflect.KTypeProjection
-import kotlin.reflect.KVariance
-import kotlin.reflect.full.createType
 import kotlin.reflect.full.isSubtypeOf
-import kotlin.reflect.full.withNullability
 import kotlin.reflect.typeOf
 
 public fun AnyCol.isColumnGroup(): Boolean {
@@ -93,13 +90,4 @@ public fun AnyCol.isComparable(): Boolean = valuesAreComparable()
  *
  * Technically, this means the values' common type `T(?)` is a subtype of [Comparable]`<in T>(?)`
  */
-public fun AnyCol.valuesAreComparable(): Boolean =
-    isValueColumn() &&
-        isSubtypeOf(
-            Comparable::class.createType(
-                arguments = listOf(
-                    KTypeProjection(KVariance.IN, type().withNullability(false)),
-                ),
-                nullable = hasNulls(),
-            ),
-        )
+public fun AnyCol.valuesAreComparable(): Boolean = isValueColumn() && type().isIntraComparable()

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/Defaults.kt

@@ -1,7 +1,7 @@
 package org.jetbrains.kotlinx.dataframe.api
 
 @PublishedApi
-internal val skipNA_default: Boolean = false
+internal val skipNaN_default: Boolean = false
 
 @PublishedApi
 internal val ddof_default: Int = 1

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/Nulls.kt

@@ -18,6 +18,8 @@ import org.jetbrains.kotlinx.dataframe.documentation.NaN
 import org.jetbrains.kotlinx.dataframe.documentation.SelectingColumns
 import org.jetbrains.kotlinx.dataframe.get
 import org.jetbrains.kotlinx.dataframe.typeClass
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 import kotlin.reflect.KProperty
 
 // region fillNulls
@@ -300,6 +302,14 @@ public fun <T, C> DataFrame<T>.fillNulls(vararg columns: ColumnReference<C>): Up
 
 internal inline val Any?.isNaN: Boolean get() = (this is Double && isNaN()) || (this is Float && isNaN())
 
+@JvmName("isNaWithContract")
+@Suppress("NOTHING_TO_INLINE")
+@OptIn(ExperimentalContracts::class)
+internal inline fun <T : Any?> T.isNA(): Boolean {
+    contract { returns(false) implies (this@isNA != null) }
+    return isNA
+}
+
 internal inline val Any?.isNA: Boolean
     get() = when (this) {
         null -> true

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/groupBy.kt

@@ -109,4 +109,5 @@ public class ReducedGroupBy<T, G>(
     override fun toString(): String = "ReducedGroupBy(groupBy=$groupBy, reducer=$reducer)"
 }
 
+@PublishedApi
 internal fun <T, G> GroupBy<T, G>.reduce(reducer: Selector<DataFrame<G>, DataRow<G>?>) = ReducedGroupBy(this, reducer)