move impl fixes

Author: AndreiKingsley

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

@@ -46,25 +46,13 @@ internal fun <T, C> MoveClause<T, C>.afterOrBefore(column: ColumnSelector<T, *>,
     val refNode = removeRoot.getOrPut(targetPath) {
         val path = it.asList()
 
-        // Find the group reference (if any) and adjust the path
-        val groupRefIndex = path.indexOfFirst { it.isEmpty() }
+        // Get parent of a target path
+        val effectivePath = path.dropLast(1)
 
-        // Calculate effective path and column name based on group reference
-        val effectivePath = if (groupRefIndex >= 0) {
-            // Nested column reference
-            path.take(groupRefIndex)
-        } else {
-            path.dropLast(1)
-        }
-
-        val columnName = if (groupRefIndex >= 0) {
-            // Use the next segment after group reference, or previous if no next segment
-            path.getOrNull(groupRefIndex + 1) ?: path[groupRefIndex - 1]
-        } else {
-            path.last()
-        }
+        // Get column name (last segment)
+        val columnName = path.last()
 
-        // Get the parent group using ColumnPath
+        // Get the parent
         val parent = if (effectivePath.isEmpty()) {
             df
         } else {

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

@@ -133,23 +133,23 @@ class MoveTests {
         // Simple case: direct parent-child relationship
         shouldThrow<IllegalArgumentException> {
             grouped.move("a").after { "a"["b"] }
-        }.message shouldBe "Cannot move column 'a' after its child column 'a/b'"
+        }.message shouldBe "Cannot move column 'a' after its own child column 'a/b'"
 
         // Nested case: deeper parent-child relationship
         shouldThrow<IllegalArgumentException> {
             grouped.move("a").after { "a"["c"]["d"] }
-        }.message shouldBe "Cannot move column 'a' after its child column 'a/c/d'"
+        }.message shouldBe "Cannot move column 'a' after its own child column 'a/c/d'"
 
         // Group case: moving group after its nested column
         shouldThrow<IllegalArgumentException> {
             grouped.move { "a"["c"] }.after { "a"["c"]["d"] }
-        }.message shouldBe "Cannot move column 'a/c' after its child column 'a/c/d'"
+        }.message shouldBe "Cannot move column 'a/c' after its own child column 'a/c/d'"
     }
 
     @Test
     fun `should throw when moving column after itself`() {
         shouldThrow<IllegalArgumentException> {
             grouped.move { "a"["b"] }.after { "a"["b"] }
-        }.message shouldBe "Cannot move column 'a/b' after its child column 'a/b'"
+        }.message shouldBe "Cannot move column 'a/b' after its own child column 'a/b'"
     }
 }