Rename all remaining MapColumn to ColumnGroup

Author: koperagen

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

@@ -67,7 +67,7 @@ internal fun <A, B> DataFrame<A>.joinImpl(
 
     require(leftJoinColumns.size == rightJoinColumns.size)
 
-    // replace all MapColumns in join with nested columns, matching by column path
+    // replace all ColumnGroups in join with nested columns, matching by column path
     val allLeftJoinColumns = mutableListOf<ColumnWithPath<*>>()
     val allRightJoinColumns = mutableListOf<ColumnWithPath<*>>()
 
@@ -220,7 +220,7 @@ internal fun <A, B> DataFrame<A>.joinImpl(
         val newColumn = when (srcColumn.kind) {
             ColumnKind.Value -> DataColumn.createValueColumn(srcColumn.name, columnValues.asList(), srcColumn.type.withNullability(hasNulls))
             ColumnKind.Frame -> DataColumn.createFrameColumn(srcColumn.name, columnValues.asList() as List<AnyFrame>)
-            ColumnKind.Group -> error("Unexpected MapColumn at path ${srcColumn.path}")
+            ColumnKind.Group -> error("Unexpected ColumnGroup at path ${srcColumn.path}")
         }
         srcColumn.path to newColumn
     }

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

@@ -75,7 +75,7 @@ internal fun <T> DataColumn<T>.updateWith(values: List<T>): DataColumn<T> = when
                     null -> null
                     is List<*> -> it[colIndex]
                     is AnyRow -> it.getOrNull(col.name)
-                    else -> require(false) { "Can not add value '$it' to MapColumn" }
+                    else -> require(false) { "Can not add value '$it' to ColumnGroup" }
                 }
             }
             col.updateWith(newValues)