Add CellKind and handle DataFrameConvertable cells

Implemented the `CellKind` enum with a `DataFrameConvertable` type. Updated JSON writing logic to handle `DataFrameConvertable` cells and added utility function to check if an object is convertible to DataFrame.

Author: ermolenkodev

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/columns/CellKind.kt

@@ -0,0 +1,7 @@
+package org.jetbrains.kotlinx.dataframe.columns
+
+public enum class CellKind {
+    DataFrameConvertable {
+        override fun toString(): String = "DataFrameConvertable"
+    },
+}

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/io/writeJson.kt

@@ -22,6 +22,7 @@ import org.jetbrains.kotlinx.dataframe.api.isList
 import org.jetbrains.kotlinx.dataframe.api.rows
 import org.jetbrains.kotlinx.dataframe.api.schema
 import org.jetbrains.kotlinx.dataframe.api.take
+import org.jetbrains.kotlinx.dataframe.columns.CellKind
 import org.jetbrains.kotlinx.dataframe.columns.ColumnGroup
 import org.jetbrains.kotlinx.dataframe.columns.ColumnKind
 import org.jetbrains.kotlinx.dataframe.columns.FrameColumn
@@ -38,6 +39,8 @@ import org.jetbrains.kotlinx.dataframe.impl.io.SerializationKeys.VERSION
 import org.jetbrains.kotlinx.dataframe.io.ARRAY_COLUMN_NAME
 import org.jetbrains.kotlinx.dataframe.io.Base64ImageEncodingOptions
 import org.jetbrains.kotlinx.dataframe.io.VALUE_COLUMN_NAME
+import org.jetbrains.kotlinx.dataframe.jupyter.KotlinNotebookPluginUtils
+import org.jetbrains.kotlinx.dataframe.jupyter.KotlinNotebookPluginUtils.isDataframeConvertable
 import org.jetbrains.kotlinx.dataframe.name
 import org.jetbrains.kotlinx.dataframe.ncol
 import org.jetbrains.kotlinx.dataframe.nrow
@@ -168,6 +171,22 @@ internal fun encodeValue(
     imageEncodingOptions: Base64ImageEncodingOptions? = null,
 ): JsonElement =
     when {
+        isDataframeConvertable(col[index]) -> if (col[index] == null) {
+            JsonPrimitive(null)
+        } else {
+            val data = encodeFrameWithMetadata(
+                KotlinNotebookPluginUtils.convertToDataFrame(col[index]!!),
+                null,
+                imageEncodingOptions,
+            )
+            buildJsonObject {
+                put(DATA, data)
+                putJsonObject(METADATA) {
+                    put(KIND, JsonPrimitive(CellKind.DataFrameConvertable.toString()))
+                }
+            }
+        }
+
         col.isList() -> col[index]?.let { list ->
             val values = (list as List<*>).map { convert(it) }
             JsonArray(values)

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/jupyter/KotlinNotebookPluginUtils.kt

@@ -101,6 +101,36 @@ public object KotlinNotebookPluginUtils {
             }.toColumnSet()
         }
 
+    internal fun isDataframeConvertable(dataframeLike: Any?): Boolean =
+        when (dataframeLike) {
+            is Pivot<*>,
+            is ReducedGroupBy<*, *>,
+            is ReducedPivot<*>,
+            is PivotGroupBy<*>,
+            is ReducedPivotGroupBy<*>,
+            is SplitWithTransform<*, *, *>,
+            is Split<*, *>,
+            is Merge<*, *, *>,
+            is Gather<*, *, *, *>,
+            is Update<*, *>,
+            is Convert<*, *>,
+            is FormattedFrame<*>,
+            is AnyCol,
+            is AnyRow,
+            is GroupBy<*, *>,
+            is AnyFrame,
+            is DisableRowsLimitWrapper,
+            is MoveClause<*, *>,
+            is RenameClause<*, *>,
+            is ReplaceClause<*, *>,
+            is GroupClause<*, *>,
+            is InsertClause<*>,
+            is FormatClause<*, *>,
+            -> true
+
+            else -> false
+        }
+
     /**
      * Converts [dataframeLike] to [AnyFrame].
      * If [dataframeLike] is already [AnyFrame] then it is returned as is.

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

@@ -0,0 +1,7 @@
+package org.jetbrains.kotlinx.dataframe.columns
+
+public enum class CellKind {
+    DataFrameConvertable {
+        override fun toString(): String = "DataFrameConvertable"
+    },
+}

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/io/writeJson.kt

@@ -22,6 +22,7 @@ import org.jetbrains.kotlinx.dataframe.api.isList
 import org.jetbrains.kotlinx.dataframe.api.rows
 import org.jetbrains.kotlinx.dataframe.api.schema
 import org.jetbrains.kotlinx.dataframe.api.take
+import org.jetbrains.kotlinx.dataframe.columns.CellKind
 import org.jetbrains.kotlinx.dataframe.columns.ColumnGroup
 import org.jetbrains.kotlinx.dataframe.columns.ColumnKind
 import org.jetbrains.kotlinx.dataframe.columns.FrameColumn
@@ -38,6 +39,8 @@ import org.jetbrains.kotlinx.dataframe.impl.io.SerializationKeys.VERSION
 import org.jetbrains.kotlinx.dataframe.io.ARRAY_COLUMN_NAME
 import org.jetbrains.kotlinx.dataframe.io.Base64ImageEncodingOptions
 import org.jetbrains.kotlinx.dataframe.io.VALUE_COLUMN_NAME
+import org.jetbrains.kotlinx.dataframe.jupyter.KotlinNotebookPluginUtils
+import org.jetbrains.kotlinx.dataframe.jupyter.KotlinNotebookPluginUtils.isDataframeConvertable
 import org.jetbrains.kotlinx.dataframe.name
 import org.jetbrains.kotlinx.dataframe.ncol
 import org.jetbrains.kotlinx.dataframe.nrow
@@ -168,6 +171,22 @@ internal fun encodeValue(
     imageEncodingOptions: Base64ImageEncodingOptions? = null,
 ): JsonElement =
     when {
+        isDataframeConvertable(col[index]) -> if (col[index] == null) {
+            JsonPrimitive(null)
+        } else {
+            val data = encodeFrameWithMetadata(
+                KotlinNotebookPluginUtils.convertToDataFrame(col[index]!!),
+                null,
+                imageEncodingOptions,
+            )
+            buildJsonObject {
+                put(DATA, data)
+                putJsonObject(METADATA) {
+                    put(KIND, JsonPrimitive(CellKind.DataFrameConvertable.toString()))
+                }
+            }
+        }
+
         col.isList() -> col[index]?.let { list ->
             val values = (list as List<*>).map { convert(it) }
             JsonArray(values)

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/jupyter/KotlinNotebookPluginUtils.kt

@@ -101,6 +101,36 @@ public object KotlinNotebookPluginUtils {
             }.toColumnSet()
         }
 
+    internal fun isDataframeConvertable(dataframeLike: Any?): Boolean =
+        when (dataframeLike) {
+            is Pivot<*>,
+            is ReducedGroupBy<*, *>,
+            is ReducedPivot<*>,
+            is PivotGroupBy<*>,
+            is ReducedPivotGroupBy<*>,
+            is SplitWithTransform<*, *, *>,
+            is Split<*, *>,
+            is Merge<*, *, *>,
+            is Gather<*, *, *, *>,
+            is Update<*, *>,
+            is Convert<*, *>,
+            is FormattedFrame<*>,
+            is AnyCol,
+            is AnyRow,
+            is GroupBy<*, *>,
+            is AnyFrame,
+            is DisableRowsLimitWrapper,
+            is MoveClause<*, *>,
+            is RenameClause<*, *>,
+            is ReplaceClause<*, *>,
+            is GroupClause<*, *>,
+            is InsertClause<*>,
+            is FormatClause<*, *>,
+            -> true
+
+            else -> false
+        }
+
     /**
      * Converts [dataframeLike] to [AnyFrame].
      * If [dataframeLike] is already [AnyFrame] then it is returned as is.