Add support for DataFrame sum operation with tests

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/sum.kt

@@ -125,10 +125,13 @@ public fun AnyRow.rowSumOf(type: KType, skipNaN: Boolean = skipNaNDefault): Numb
 // endregion
 
 // region DataFrame
-
+@Refine
+@Interpretable("Sum0")
 public fun <T> DataFrame<T>.sum(skipNaN: Boolean = skipNaNDefault): DataRow<T> =
     sumFor(skipNaN, primitiveOrMixedNumberColumns())
 
+@Refine
+@Interpretable("Sum1")
 public fun <T, C : Number?> DataFrame<T>.sumFor(
     skipNaN: Boolean = skipNaNDefault,
     columns: ColumnsForAggregateSelector<T, C>,

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/Aggregator.kt

@@ -37,12 +37,11 @@ import kotlin.reflect.full.withNullability
  * @param Return The type of the resulting value. Can optionally be nullable.
  * @see [invoke]
  */
-@PublishedApi
-internal class Aggregator<in Value : Any, out Return : Any?>(
-    val aggregationHandler: AggregatorAggregationHandler<Value, Return>,
-    val inputHandler: AggregatorInputHandler<Value, Return>,
-    val multipleColumnsHandler: AggregatorMultipleColumnsHandler<Value, Return>,
-    val name: String,
+public class Aggregator<in Value : Any, out Return : Any?>(
+    public val aggregationHandler: AggregatorAggregationHandler<Value, Return>,
+    public val inputHandler: AggregatorInputHandler<Value, Return>,
+    public val multipleColumnsHandler: AggregatorMultipleColumnsHandler<Value, Return>,
+    public val name: String,
 ) : AggregatorInputHandler<Value, Return> by inputHandler,
     AggregatorMultipleColumnsHandler<Value, Return> by multipleColumnsHandler,
     AggregatorAggregationHandler<Value, Return> by aggregationHandler {
@@ -96,7 +95,7 @@ internal class Aggregator<in Value : Any, out Return : Any?>(
 internal fun <Value : Any, Return : Any?> Aggregator<Value, Return>.aggregate(
     values: Sequence<Value?>,
     valueType: ValueType,
-) = aggregateSequence(values, valueType)
+): Return = aggregateSequence(values, valueType)
 
 /**
  * Performs aggregation on the given [values], taking [valueType] into account.
@@ -106,7 +105,7 @@ internal fun <Value : Any, Return : Any?> Aggregator<Value, Return>.aggregate(
 internal fun <Value : Any, Return : Any?> Aggregator<Value, Return>.aggregate(
     values: Sequence<Value?>,
     valueType: KType,
-) = aggregate(values, valueType.toValueType(needsFullConversion = false))
+): Return = aggregate(values, valueType.toValueType(needsFullConversion = false))
 
 /**
  * If the specific [ValueType] of the input is not known, but you still want to call [aggregate],

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorAggregationHandler.kt

@@ -11,8 +11,7 @@ import kotlin.reflect.KType
  * It also provides information on which return type will be given, as [KType], given a [value type][ValueType].
  * It can also provide the index of the result in the input values if it is a selecting aggregator.
  */
-@PublishedApi
-internal interface AggregatorAggregationHandler<in Value : Any, out Return : Any?> : AggregatorHandler<Value, Return> {
+public interface AggregatorAggregationHandler<in Value : Any, out Return : Any?> : AggregatorHandler<Value, Return> {
 
     /**
      * Base function of [Aggregator].
@@ -23,13 +22,13 @@ internal interface AggregatorAggregationHandler<in Value : Any, out Return : Any
      *
      * When the exact [valueType] is unknown, use [calculateValueType] or [aggregateCalculatingValueType].
      */
-    fun aggregateSequence(values: Sequence<Value?>, valueType: ValueType): Return
+    public fun aggregateSequence(values: Sequence<Value?>, valueType: ValueType): Return
 
     /**
      * Aggregates the data in the given column and computes a single resulting value.
      * Calls [aggregateSequence].
      */
-    fun aggregateSingleColumn(column: DataColumn<Value?>): Return =
+    public fun aggregateSingleColumn(column: DataColumn<Value?>): Return =
         aggregateSequence(
             values = column.asSequence(),
             valueType = column.type().toValueType(),
@@ -43,7 +42,7 @@ internal interface AggregatorAggregationHandler<in Value : Any, out Return : Any
      * @param emptyInput If `true`, the input values are considered empty. This often affects the return type.
      * @return The return type of [aggregateSequence] as [KType].
      */
-    fun calculateReturnType(valueType: KType, emptyInput: Boolean): KType
+    public fun calculateReturnType(valueType: KType, emptyInput: Boolean): KType
 
     /**
      * Function that can give the index of the aggregation result in the input [values], if it applies.
@@ -54,5 +53,5 @@ internal interface AggregatorAggregationHandler<in Value : Any, out Return : Any
      *
      * Defaults to `-1`.
      */
-    fun indexOfAggregationResultSingleSequence(values: Sequence<Value?>, valueType: ValueType): Int
+    public fun indexOfAggregationResultSingleSequence(values: Sequence<Value?>, valueType: ValueType): Int
 }

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorHandler.kt

@@ -7,16 +7,16 @@ package org.jetbrains.kotlinx.dataframe.impl.aggregation.aggregators
  * the [init] function of each [AggregatorAggregationHandlers][AggregatorAggregationHandler] is called,
  * which allows the handler to refer to [Aggregator] instance via [aggregator].
  */
-internal interface AggregatorHandler<in Value : Any, out Return : Any?> {
+public interface AggregatorHandler<in Value : Any, out Return : Any?> {
 
     /**
      * Reference to the aggregator instance.
      *
      * Can only be used once [init] has run.
      */
-    var aggregator: Aggregator<@UnsafeVariance Value, @UnsafeVariance Return>?
+    public var aggregator: Aggregator<@UnsafeVariance Value, @UnsafeVariance Return>?
 
-    fun init(aggregator: Aggregator<@UnsafeVariance Value, @UnsafeVariance Return>) {
+    public fun init(aggregator: Aggregator<@UnsafeVariance Value, @UnsafeVariance Return>) {
         this.aggregator = aggregator
     }
 }

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorInputHandler.kt

@@ -8,13 +8,13 @@ import kotlin.reflect.KType
  * It can also calculate a specific [value type][ValueType] from the input values or input types
  * if the (specific) type is not known.
  */
-internal interface AggregatorInputHandler<in Value : Any, out Return : Any?> : AggregatorHandler<Value, Return> {
+public interface AggregatorInputHandler<in Value : Any, out Return : Any?> : AggregatorHandler<Value, Return> {
 
     /**
      * If the specific [ValueType] of the input is not known, but you still want to call [aggregate],
      * this function can be called to calculate it by combining the set of known [valueTypes].
      */
-    fun calculateValueType(valueTypes: Set<KType>): ValueType
+    public fun calculateValueType(valueTypes: Set<KType>): ValueType
 
     /**
      * WARNING: HEAVY!
@@ -23,7 +23,7 @@ internal interface AggregatorInputHandler<in Value : Any, out Return : Any?> : A
      * this function can be called to calculate it by getting the types of [values] at runtime.
      * This is heavy because it uses reflection on each value.
      */
-    fun calculateValueType(values: Sequence<Value?>): ValueType
+    public fun calculateValueType(values: Sequence<Value?>): ValueType
 
     /**
      * Preprocesses the input values before aggregation.
@@ -32,7 +32,7 @@ internal interface AggregatorInputHandler<in Value : Any, out Return : Any?> : A
      *
      * @return A pair of the preprocessed values and the (potentially new) type of the values.
      */
-    fun preprocessAggregation(
+    public fun preprocessAggregation(
         values: Sequence<Value?>,
         valueType: ValueType,
     ): Pair<Sequence<@UnsafeVariance Value?>, KType>

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorMultipleColumnsHandler.kt

@@ -10,14 +10,14 @@ import kotlin.reflect.KType
  * [AggregatorAggregationHandler].
  * It can also calculate the return type of the aggregation given all input column types.
  */
-internal interface AggregatorMultipleColumnsHandler<in Value : Any, out Return : Any?> :
+public interface AggregatorMultipleColumnsHandler<in Value : Any, out Return : Any?> :
     AggregatorHandler<Value, Return> {
 
     /**
      * Aggregates the data in the multiple given columns and computes a single resulting value.
      * Calls [Aggregator.aggregateSequence] or [Aggregator.aggregateSingleColumn].
      */
-    fun aggregateMultipleColumns(columns: Sequence<DataColumn<Value?>>): Return
+    public fun aggregateMultipleColumns(columns: Sequence<DataColumn<Value?>>): Return
 
     /**
      * Function that can give the return type of [aggregateMultipleColumns], given types of the columns.
@@ -26,5 +26,5 @@ internal interface AggregatorMultipleColumnsHandler<in Value : Any, out Return :
      * @param colTypes The types of the input columns.
      * @param colsEmpty If `true`, all the input columns are considered empty. This often affects the return type.
      */
-    fun calculateReturnTypeMultipleColumns(colTypes: Set<KType>, colsEmpty: Boolean): KType
+    public fun calculateReturnTypeMultipleColumns(colTypes: Set<KType>, colsEmpty: Boolean): KType
 }

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorOptionSwitch.kt

@@ -6,21 +6,20 @@ package org.jetbrains.kotlinx.dataframe.impl.aggregation.aggregators
  * Aggregators are cached by their parameter value.
  * @see AggregatorOptionSwitch2
  */
-@PublishedApi
-internal class AggregatorOptionSwitch1<in Param1, in Value : Any, out Return : Any?>(
-    val name: String,
-    val getAggregator: (param1: Param1) -> AggregatorProvider<Value, Return>,
+public class AggregatorOptionSwitch1<in Param1, in Value : Any, out Return : Any?>(
+    public val name: String,
+    public val getAggregator: (param1: Param1) -> AggregatorProvider<Value, Return>,
 ) {
 
     private val cache: MutableMap<Param1, Aggregator<Value, Return>> = mutableMapOf()
 
-    operator fun invoke(param1: Param1): Aggregator<Value, Return> =
+    public operator fun invoke(param1: Param1): Aggregator<Value, @UnsafeVariance Return> =
         cache.getOrPut(param1) {
             getAggregator(param1).create(name)
         }
 
     @Suppress("FunctionName")
-    companion object {
+    public companion object {
 
         /**
          * Creates [AggregatorOptionSwitch1].
@@ -31,9 +30,10 @@ internal class AggregatorOptionSwitch1<in Param1, in Value : Any, out Return : A
          *   MyAggregator.Factory(param1)
          * }
          */
-        fun <Param1, Value : Any, Return : Any?> Factory(
+        public fun <Param1, Value : Any, Return : Any?> Factory(
             getAggregator: (param1: Param1) -> AggregatorProvider<Value, Return>,
-        ) = Provider { name -> AggregatorOptionSwitch1(name, getAggregator) }
+        ): Provider<AggregatorOptionSwitch1<Param1, Value, Return>> =
+            Provider { name -> AggregatorOptionSwitch1(name, getAggregator) }
     }
 }
 
@@ -43,21 +43,20 @@ internal class AggregatorOptionSwitch1<in Param1, in Value : Any, out Return : A
  * Aggregators are cached by their parameter values.
  * @see AggregatorOptionSwitch1
  */
-@PublishedApi
-internal class AggregatorOptionSwitch2<in Param1, in Param2, in Value : Any, out Return : Any?>(
-    val name: String,
-    val getAggregator: (param1: Param1, param2: Param2) -> AggregatorProvider<Value, Return>,
+public class AggregatorOptionSwitch2<in Param1, in Param2, in Value : Any, out Return : Any?>(
+    public val name: String,
+    public val getAggregator: (param1: Param1, param2: Param2) -> AggregatorProvider<Value, Return>,
 ) {
 
     private val cache: MutableMap<Pair<Param1, Param2>, Aggregator<Value, Return>> = mutableMapOf()
 
-    operator fun invoke(param1: Param1, param2: Param2): Aggregator<Value, Return> =
+    public operator fun invoke(param1: Param1, param2: Param2): Aggregator<Value, @UnsafeVariance Return> =
         cache.getOrPut(param1 to param2) {
             getAggregator(param1, param2).create(name)
         }
 
     @Suppress("FunctionName")
-    companion object {
+    public companion object {
 
         /**
          * Creates [AggregatorOptionSwitch2].
@@ -68,7 +67,7 @@ internal class AggregatorOptionSwitch2<in Param1, in Param2, in Value : Any, out
          *   MyAggregator.Factory(param1, param2)
          * }
          */
-        fun <Param1, Param2, Value : Any, Return : Any?> Factory(
+        internal fun <Param1, Param2, Value : Any, Return : Any?> Factory(
             getAggregator: (param1: Param1, param2: Param2) -> AggregatorProvider<Value, Return>,
         ) = Provider { name -> AggregatorOptionSwitch2(name, getAggregator) }
     }

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorProvider.kt

@@ -10,9 +10,9 @@ import kotlin.reflect.KProperty
  * val myNamedValue by MyFactory
  * ```
  */
-internal fun interface Provider<out T> {
+public fun interface Provider<out T> {
 
-    fun create(name: String): T
+    public fun create(name: String): T
 }
 
 internal operator fun <T> Provider<T>.getValue(obj: Any?, property: KProperty<*>): T = create(property.name)
@@ -25,4 +25,5 @@ internal operator fun <T> Provider<T>.getValue(obj: Any?, property: KProperty<*>
  * val myAggregator by MyAggregator.Factory
  * ```
  */
-internal fun interface AggregatorProvider<in Value : Any, out Return : Any?> : Provider<Aggregator<Value, Return>>
+public fun interface AggregatorProvider<in Value : Any, out Return : Any?> :
+    Provider<Aggregator<Value, @UnsafeVariance Return>>

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/Aggregators.kt

@@ -27,8 +27,7 @@ import org.jetbrains.kotlinx.dataframe.math.stdTypeConversion
 import org.jetbrains.kotlinx.dataframe.math.sum
 import org.jetbrains.kotlinx.dataframe.math.sumTypeConversion
 
-@PublishedApi
-internal object Aggregators {
+public object Aggregators {
 
     // TODO these might need some small refactoring
 
@@ -112,7 +111,7 @@ internal object Aggregators {
 
     // T: Comparable<T> -> T?
     // T : Comparable<T & Any>? -> T?
-    fun <T : Comparable<T & Any>?> min(skipNaN: Boolean): Aggregator<T & Any, T?> = min.invoke(skipNaN).cast2()
+    public fun <T : Comparable<T & Any>?> min(skipNaN: Boolean): Aggregator<T & Any, T?> = min.invoke(skipNaN).cast2()
 
     private val min by withOneOption { skipNaN: Boolean ->
         twoStepSelectingForAny<Comparable<Any>, Comparable<Any>?>(
@@ -124,7 +123,7 @@ internal object Aggregators {
 
     // T: Comparable<T> -> T?
     // T : Comparable<T & Any>? -> T?
-    fun <T : Comparable<T & Any>?> max(skipNaN: Boolean): Aggregator<T & Any, T?> = max.invoke(skipNaN).cast2()
+    public fun <T : Comparable<T & Any>?> max(skipNaN: Boolean): Aggregator<T & Any, T?> = max.invoke(skipNaN).cast2()
 
     private val max by withOneOption { skipNaN: Boolean ->
         twoStepSelectingForAny<Comparable<Any>, Comparable<Any>?>(
@@ -135,36 +134,41 @@ internal object Aggregators {
     }
 
     // T: Number? -> Double
-    val std by withTwoOptions { skipNaN: Boolean, ddof: Int ->
+    public val std: AggregatorOptionSwitch2<Boolean, Int, Number, Double> by withTwoOptions {
+        skipNaN: Boolean,
+        ddof: Int,
+        ->
         flattenReducingForNumbers(stdTypeConversion) { type ->
             std(type, skipNaN, ddof)
         }
     }
 
     // step one: T: Number? -> Double
     // step two: Double -> Double
-    val mean by withOneOption { skipNaN: Boolean ->
+    public val mean: AggregatorOptionSwitch1<Boolean, Number, Double> by withOneOption { skipNaN: Boolean ->
         twoStepReducingForNumbers(meanTypeConversion) { type ->
             mean(type, skipNaN)
         }
     }
 
     // T : primitive Number? -> Double?
     // T : Comparable<T & Any>? -> T?
-    fun <T> percentileCommon(
+    public fun <T> percentileCommon(
         percentile: Double,
         skipNaN: Boolean,
     ): Aggregator<T & Any, T?>
         where T : Comparable<T & Any>? =
         this.percentile.invoke(percentile, skipNaN).cast2()
 
     // T : Comparable<T & Any>? -> T?
-    fun <T> percentileComparables(percentile: Double): Aggregator<T & Any, T?>
+    public fun <T> percentileComparables(
+        percentile: Double,
+    ): Aggregator<T & Any, T?>
         where T : Comparable<T & Any>? =
         percentileCommon<T>(percentile, skipNaNDefault).cast2()
 
     // T : primitive Number? -> Double?
-    fun <T> percentileNumbers(
+    public fun <T> percentileNumbers(
         percentile: Double,
         skipNaN: Boolean,
     ): Aggregator<T & Any, Double?>
@@ -182,17 +186,17 @@ internal object Aggregators {
 
     // T : primitive Number? -> Double?
     // T : Comparable<T & Any>? -> T?
-    fun <T> medianCommon(skipNaN: Boolean): Aggregator<T & Any, T?>
+    public fun <T> medianCommon(skipNaN: Boolean): Aggregator<T & Any, T?>
         where T : Comparable<T & Any>? =
         median.invoke(skipNaN).cast2()
 
     // T : Comparable<T & Any>? -> T?
-    fun <T> medianComparables(): Aggregator<T & Any, T?>
+    public fun <T> medianComparables(): Aggregator<T & Any, T?>
         where T : Comparable<T & Any>? =
         medianCommon<T>(skipNaNDefault).cast2()
 
     // T : primitive Number? -> Double?
-    fun <T> medianNumbers(
+    public fun <T> medianNumbers(
         skipNaN: Boolean,
     ): Aggregator<T & Any, Double?>
         where T : Comparable<T & Any>?, T : Number? =
@@ -211,7 +215,7 @@ internal object Aggregators {
     // Byte -> Int
     // Short -> Int
     // Nothing -> Double
-    val sum by withOneOption { skipNaN: Boolean ->
+    public val sum: AggregatorOptionSwitch1<Boolean, Number, Number> by withOneOption { skipNaN: Boolean ->
         twoStepReducingForNumbers(sumTypeConversion) { type ->
             sum(type, skipNaN)
         }

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/ValueType.kt

@@ -10,6 +10,6 @@ import kotlin.reflect.KType
  *   for the values to become the correct value type. If `false`, the values are already the right type,
  *   or a simple cast will suffice.
  */
-internal data class ValueType(val kType: KType, val needsFullConversion: Boolean = false)
+public data class ValueType(val kType: KType, val needsFullConversion: Boolean = false)
 
 internal fun KType.toValueType(needsFullConversion: Boolean = false): ValueType = ValueType(this, needsFullConversion)

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/multipleColumnsHandlers/TwoStepMultipleColumnsHandler.kt

@@ -31,7 +31,7 @@ import kotlin.reflect.KType
  *   If not supplied, the handler of the first step is reused.
  * @see [FlatteningMultipleColumnsHandler]
  */
-internal class TwoStepMultipleColumnsHandler<in Value : Any, out Return : Any?>(
+internal class TwoStepMultipleColumnsHandler<in Value : Any, Return : Any?>(
     stepTwoAggregationHandler: AggregatorAggregationHandler<Return & Any, Return>? = null,
     stepTwoInputHandler: AggregatorInputHandler<Return & Any, Return>? = null,
 ) : AggregatorMultipleColumnsHandler<Value, Return> {