Make GroupBy.Entry.group not nullable. Remove redundant GroupBy.forEach overload.

Author: nikitinas

src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/forEach.kt

@@ -2,7 +2,6 @@ package org.jetbrains.kotlinx.dataframe.api
 
 import org.jetbrains.kotlinx.dataframe.DataColumn
 import org.jetbrains.kotlinx.dataframe.DataFrame
-import org.jetbrains.kotlinx.dataframe.DataRow
 import org.jetbrains.kotlinx.dataframe.RowExpression
 import org.jetbrains.kotlinx.dataframe.columns.values
 
@@ -22,15 +21,9 @@ public fun <T> DataFrame<T>.forEach(action: RowExpression<T, Unit>): Unit = rows
 
 // region GroupBy
 
-public fun <T, G> GroupBy<T, G>.forEach(body: (GroupBy.Entry<T, G>) -> Unit): Unit = forEach { key, group ->
-    body(
-        GroupBy.Entry(key, group)
-    )
+public fun <T, G> GroupBy<T, G>.forEach(body: (GroupBy.Entry<T, G>) -> Unit): Unit = keys.forEach { key ->
+    val group = groups[key.index()]
+    body(GroupBy.Entry(key, group))
 }
-public fun <T, G> GroupBy<T, G>.forEach(body: (key: DataRow<T>, group: DataFrame<G>?) -> Unit): Unit =
-    keys.forEach { row ->
-        val group = groups[row.index()]
-        body(row, group)
-    }
 
 // endregion

src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/groupBy.kt

@@ -66,7 +66,7 @@ public interface GroupBy<out T, out G> : Grouped<G> {
 
     public fun filter(predicate: GroupedRowFilter<T, G>): GroupBy<T, G>
 
-    public data class Entry<T, G>(val key: DataRow<T>, val group: DataFrame<G>?)
+    public data class Entry<T, G>(val key: DataRow<T>, val group: DataFrame<G>)
 
     public companion object {
         internal val groupedColumnAccessor = column<AnyFrame>("group")

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

@@ -81,7 +81,7 @@ internal fun <T, R> aggregatePivot(
     val effectiveInward = inward ?: if (aggregator.hasGroupingKeys) true else (pivotSequences.distinctBy { it.first().column.path }.count() > 1)
     pivotSequences.forEach { pivotColumns ->
 
-        aggregator.df.groupBy(pivotColumns.map { it.column }).forEach { key, group ->
+        aggregator.df.groupBy(pivotColumns.map { it.column }).forEach { (key, group) ->
 
             val pathNames = mutableListOf<String>()
             key.values().forEachIndexed { i, v ->
@@ -90,7 +90,7 @@ internal fun <T, R> aggregatePivot(
                 pathNames.add(v.toString())
             }
             val path = pathNames.toPath()
-            val builder = AggregatePivotDslImpl(group!!)
+            val builder = AggregatePivotDslImpl(group)
             val result = body(builder, builder)
             val hasResult = result != null && result != Unit
 

tests/src/test/kotlin/org/jetbrains/kotlinx/dataframe/testSets/person/DataFrameTreeTests.kt

@@ -40,7 +40,6 @@ import org.jetbrains.kotlinx.dataframe.api.explode
 import org.jetbrains.kotlinx.dataframe.api.expr
 import org.jetbrains.kotlinx.dataframe.api.filter
 import org.jetbrains.kotlinx.dataframe.api.forEach
-import org.jetbrains.kotlinx.dataframe.api.forEach
 import org.jetbrains.kotlinx.dataframe.api.frameColumn
 import org.jetbrains.kotlinx.dataframe.api.getColumnGroup
 import org.jetbrains.kotlinx.dataframe.api.getColumnPath