Provide filter overload to replace colGroups(predicate<ColumnGroup>)

I prefer composition to inheritance here because changing ColumnWithPath hierarchy seems difficult,
a lot of code assumes only one possible implementation. So for the sake of only one `filter` implementation, let's introduce a simple new class

Author: koperagen

core/api/core.api

@@ -2128,6 +2128,7 @@ public abstract interface class org/jetbrains/kotlinx/dataframe/api/ExprColumnsS
 
 public abstract interface class org/jetbrains/kotlinx/dataframe/api/FilterColumnsSelectionDsl {
 	public fun filter (Lorg/jetbrains/kotlinx/dataframe/columns/ColumnSet;Lkotlin/jvm/functions/Function1;)Lorg/jetbrains/kotlinx/dataframe/columns/ColumnSet;
+	public fun filterColumnGroups (Lorg/jetbrains/kotlinx/dataframe/columns/ColumnSet;Lkotlin/jvm/functions/Function1;)Lorg/jetbrains/kotlinx/dataframe/columns/ColumnSet;
 }
 
 public abstract interface class org/jetbrains/kotlinx/dataframe/api/FilterColumnsSelectionDsl$Grammar {
@@ -5058,6 +5059,16 @@ public abstract interface class org/jetbrains/kotlinx/dataframe/columns/ColumnGr
 	public abstract fun rename (Ljava/lang/String;)Lorg/jetbrains/kotlinx/dataframe/columns/ColumnGroup;
 }
 
+public final class org/jetbrains/kotlinx/dataframe/columns/ColumnGroupWithPath {
+	public fun <init> (Lorg/jetbrains/kotlinx/dataframe/columns/ColumnGroup;Lorg/jetbrains/kotlinx/dataframe/columns/ColumnPath;)V
+	public final fun depth ()I
+	public final fun getData ()Lorg/jetbrains/kotlinx/dataframe/columns/ColumnGroup;
+	public final fun getDepth ()I
+	public final fun getName ()Ljava/lang/String;
+	public final fun getParentName ()Ljava/lang/String;
+	public final fun getPath ()Lorg/jetbrains/kotlinx/dataframe/columns/ColumnPath;
+}
+
 public class org/jetbrains/kotlinx/dataframe/columns/ColumnKind : java/lang/Enum {
 	public static final field Frame Lorg/jetbrains/kotlinx/dataframe/columns/ColumnKind;
 	public static final field Group Lorg/jetbrains/kotlinx/dataframe/columns/ColumnKind;

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

@@ -1,5 +1,6 @@
 package org.jetbrains.kotlinx.dataframe.api
 
+import org.jetbrains.kotlinx.dataframe.AnyRow
 import org.jetbrains.kotlinx.dataframe.ColumnFilter
 import org.jetbrains.kotlinx.dataframe.ColumnSelector
 import org.jetbrains.kotlinx.dataframe.ColumnsSelector
@@ -8,6 +9,7 @@ import org.jetbrains.kotlinx.dataframe.DataFrame
 import org.jetbrains.kotlinx.dataframe.Predicate
 import org.jetbrains.kotlinx.dataframe.RowFilter
 import org.jetbrains.kotlinx.dataframe.annotations.AccessApiOverload
+import org.jetbrains.kotlinx.dataframe.columns.ColumnGroupWithPath
 import org.jetbrains.kotlinx.dataframe.columns.ColumnPath
 import org.jetbrains.kotlinx.dataframe.columns.ColumnReference
 import org.jetbrains.kotlinx.dataframe.columns.ColumnSet
@@ -159,6 +161,25 @@ public interface FilterColumnsSelectionDsl {
     @Suppress("UNCHECKED_CAST")
     public fun <C> ColumnSet<C>.filter(predicate: ColumnFilter<C>): ColumnSet<C> =
         colsInternal(predicate as ColumnFilter<*>).cast()
+
+    /**
+     * ## Filter [ColumnSet]
+     *
+     * #### For example:
+     * ```kotlin
+     * df.convert {
+     *  colsAtAnyDepth().colGroups()
+     *    .filter { it.data.containsColumn("myCol")
+     * }.with { ... }
+     * ```
+     */
+    @Suppress("INAPPLICABLE_JVM_NAME")
+    @JvmName("filterColumnGroups")
+    public fun ColumnSet<AnyRow>.filter(predicate: Predicate<ColumnGroupWithPath<*>>): ColumnSet<*> =
+        colsInternal { columnWithPath ->
+            columnWithPath.isColumnGroup() &&
+                predicate(ColumnGroupWithPath(columnWithPath, columnWithPath.path))
+        }
 }
 
 // endregion

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/columns/ColumnWithPath.kt

@@ -63,3 +63,13 @@ public interface ColumnWithPath<out T> : DataColumn<T> {
 public val <T> ColumnWithPath<T>.depth: Int get() = path.depth()
 
 public fun ColumnWithPath(column: DataColumn<*>, path: ColumnPath): ColumnWithPath<*> = column.addPath(path)
+
+public class ColumnGroupWithPath<T>(public val data: ColumnGroup<T>, public val path: ColumnPath) {
+    public val name: String get() = data.name()
+
+    public val parentName: String? get() = path.parentName
+
+    public fun depth(): Int = path.depth()
+
+    public val depth: Int get() = path.depth()
+}

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/api/filter.kt

@@ -19,4 +19,12 @@ class FilterTests : ColumnsSelectionDslTests() {
         df.select { all().filter { true } } shouldBe df.select { all() }
         df.select { all().filter { false } } shouldBe df.select { none() }
     }
+
+    @Test
+    fun `filter column group`() {
+        listOf(
+            df.select { name },
+            df.select { colsAtAnyDepth().colGroups().filter { it.data.containsColumn("firstName") } }
+        )
+    }
 }