Add type argument for ColumnGroupAccessor

Author: nikitinas

src/main/kotlin/org/jetbrains/kotlinx/dataframe/aliases.kt

@@ -43,7 +43,8 @@ public typealias RowValueFilter<T, C> = RowValueExpression<T, C, Boolean>
 public typealias Column = ColumnReference<*>
 
 public typealias ColumnGroupReference = ColumnReference<AnyRow>
-public typealias ColumnGroupAccessor = ColumnAccessor<AnyRow>
+public typealias ColumnGroupAccessor<T> = ColumnAccessor<DataRow<T>>
+public typealias AnyColumnGroupAccessor = ColumnGroupAccessor<*>
 
 public typealias DoubleCol = DataColumn<Double?>
 public typealias BooleanCol = DataColumn<Boolean?>

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

@@ -190,6 +190,11 @@ public inline fun <reified T> Iterable<T>.toColumn(property: KProperty<T>): Data
 
 public fun Iterable<String>.toPath(): ColumnPath = ColumnPath(asList())
 
+public fun Iterable<AnyBaseColumn>.toColumnGroup(name: String): ColumnGroup<*> = dataFrameOf(this).asColumnGroup(name)
+public fun <T> Iterable<AnyBaseColumn>.toColumnGroup(column: ColumnGroupAccessor<T>): ColumnGroup<T> = dataFrameOf(this).cast<T>().asColumnGroup(column)
+
+public fun <T> Iterable<AnyBaseColumn>.toColumnGroupOf(name: String): ColumnGroup<T> = toColumnGroup(name).cast()
+
 // endregion
 
 // region DataFrame
@@ -201,7 +206,7 @@ public fun <T> DataFrame<T>.asColumnGroup(name: String = ""): ColumnGroup<T> = w
     else -> DataColumn.createColumnGroup(name, this)
 }
 
-public fun <T> DataFrame<T>.asColumnGroup(column: ColumnGroupAccessor): ColumnGroup<*> = asColumnGroup(column.name)
+public fun <T> DataFrame<T>.asColumnGroup(column: ColumnGroupAccessor<T>): ColumnGroup<T> = asColumnGroup(column.name)
 
 // region as GroupedDataFrame
 

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

@@ -1,7 +1,7 @@
 package org.jetbrains.kotlinx.dataframe.api
 
+import org.jetbrains.kotlinx.dataframe.AnyColumnGroupAccessor
 import org.jetbrains.kotlinx.dataframe.Column
-import org.jetbrains.kotlinx.dataframe.ColumnGroupAccessor
 import org.jetbrains.kotlinx.dataframe.ColumnsSelector
 import org.jetbrains.kotlinx.dataframe.DataFrame
 import org.jetbrains.kotlinx.dataframe.columns.ColumnWithPath
@@ -27,7 +27,7 @@ public infix fun <T, C> GroupClause<T, C>.into(column: ColumnsSelectionDsl<T>.(C
 @JvmName("intoColumn")
 public infix fun <T, C> GroupClause<T, C>.into(column: ColumnsSelectionDsl<T>.(ColumnWithPath<C>) -> Column): DataFrame<T> = df.move(columns).under(column)
 public infix fun <T, C> GroupClause<T, C>.into(column: String): DataFrame<T> = into(columnGroup().named(column))
-public infix fun <T, C> GroupClause<T, C>.into(column: ColumnGroupAccessor): DataFrame<T> = df.move(columns).under(column)
+public infix fun <T, C> GroupClause<T, C>.into(column: AnyColumnGroupAccessor): DataFrame<T> = df.move(columns).under(column)
 public infix fun <T, C> GroupClause<T, C>.into(column: KProperty<*>): DataFrame<T> = into(column.columnName)
 
 // endregion

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

@@ -1,7 +1,7 @@
 package org.jetbrains.kotlinx.dataframe.api
 
+import org.jetbrains.kotlinx.dataframe.AnyColumnGroupAccessor
 import org.jetbrains.kotlinx.dataframe.Column
-import org.jetbrains.kotlinx.dataframe.ColumnGroupAccessor
 import org.jetbrains.kotlinx.dataframe.ColumnSelector
 import org.jetbrains.kotlinx.dataframe.ColumnsSelector
 import org.jetbrains.kotlinx.dataframe.DataFrame
@@ -51,7 +51,7 @@ public fun <T, C> MoveClause<T, C>.intoIndexed(
 }
 
 public fun <T, C> MoveClause<T, C>.under(column: String): DataFrame<T> = pathOf(column).let { path -> under { path } }
-public fun <T, C> MoveClause<T, C>.under(column: ColumnGroupAccessor): DataFrame<T> = column.path().let { path -> under { path } }
+public fun <T, C> MoveClause<T, C>.under(column: AnyColumnGroupAccessor): DataFrame<T> = column.path().let { path -> under { path } }
 public fun <T, C> MoveClause<T, C>.under(column: ColumnsSelectionDsl<T>.(ColumnWithPath<C>) -> Column): DataFrame<T> = moveImpl(
     under = true,
     column