Add medianBy and percentileBy to the groupBy grammar

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

@@ -124,6 +124,12 @@ internal interface GroupByDocs {
      * `| `__`.`__[**`last`**][GroupBy.last]`  \[ `**`  {  `**`rowCondition: `[`RowFilter`][RowFilter]**`  }  `**`]`
      *
      * {@include [Indent]}
+     * `| `__`.`__[**`medianBy`**][GroupBy.medianBy]**`  {  `**`rowExpression: `[`RowExpression`][RowExpression]**` }`**
+     *
+     * {@include [Indent]}
+     * `| `__`.`__[**`percentileBy`**][GroupBy.percentileBy]**`(`**`percentile: `[`Double`][Double]**`)  {  `**`rowExpression: `[`RowExpression`][RowExpression]**` }`**
+     *
+     * {@include [Indent]}
      * __`.`__[**`concat`**][ReducedGroupBy.concat]**`() `**
      *
      * {@include [Indent]}
@@ -251,8 +257,8 @@ internal interface GroupByDocs {
      *   (optionally, the first or last one that satisfies a predicate) of each group;
      * * [minBy][GroupBy.minBy] / [maxBy][GroupBy.maxBy] — take the row with the minimum or maximum value
      *   of the given [RowExpression] calculated on rows within each group;
-     * * [medianBy][GroupBy.medianBy] / [percentileBy][GroupBy.percentileBy] — take the row with
-     *   the median or specific percentile value of the given [RowExpression] calculated on rows within each group;
+     * * [medianBy][GroupBy.medianBy] / [percentileBy][GroupBy.percentileBy] — take the row at the position closest
+     *   to the estimated median/percentile index of the [RowExpression]'s results calculated on rows within each group.
      *
      * These functions return a [ReducedGroupBy], which can then be transformed into a new [DataFrame]
      * containing the reduced rows (either original or transformed) using one of the following methods:

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

@@ -86,10 +86,10 @@ internal interface PivotDocs {
      * `| `__`.`__[**`last`**][Pivot.last]`  \[ `**`{  `**`rowCondition: `[`RowFilter`][RowFilter]**`  }  `**`]`
      *
      * {@include [Indent]}
-     * `| `__`.`__[**`medianBy`**][Pivot.medianBy]**`  {  `**`column: `[`RowExpression`][RowExpression]**` }`**
+     * `| `__`.`__[**`medianBy`**][Pivot.medianBy]**`  {  `**`rowExpression: `[`RowExpression`][RowExpression]**` }`**
      *
      * {@include [Indent]}
-     * `| `__`.`__[**`percentileBy`**][Pivot.percentileBy]**`(`**`percentile: `[`Double`][Double]**`)  {  `**`column: `[`RowExpression`][RowExpression]**` }`**
+     * `| `__`.`__[**`percentileBy`**][Pivot.percentileBy]**`(`**`percentile: `[`Double`][Double]**`)  {  `**`rowExpression: `[`RowExpression`][RowExpression]**` }`**
      *
      * {@include [Indent]}
      * __`.`__[**`with`**][Pivot.with]**`  {  `**`rowExpression: `[`RowExpression`][RowExpression]**` }`**
@@ -150,8 +150,8 @@ internal interface PivotDocs {
      *   (optionally, the first or last one that satisfies a predicate) of each group;
      * * [minBy][Pivot.minBy] / [maxBy][Pivot.maxBy] — take the row with the minimum or maximum value
      *   of the given [RowExpression] evaluated on rows within each group;
-     * * [medianBy][Pivot.medianBy] / [percentileBy][Pivot.percentileBy] — take the row with
-     *   the median or a specific percentile value of the given [RowExpression] evaluated on rows within each group.
+     * * [medianBy][Pivot.medianBy] / [percentileBy][Pivot.percentileBy] — take the row at the position closest
+     *   to the estimated median/percentile index of the [RowExpression]'s results calculated on rows within each group.
      *
      * These functions return a [ReducedPivot], which can then be transformed into a new [DataFrame]
      * containing a single combined row (either using the original reduced rows or their transformed versions)

docs/StardustDocs/topics/groupBy.md

@@ -372,7 +372,7 @@ To perform a reducing operation, use the following functions:
 * [`minBy`](minBy.md) / [`maxBy`](maxBy.md) – to get from each group the row with the smallest / largest result 
 of the [`row expression`](DataRow.md#row-expressions) supplied to the function.
 
-* [`medianBy`](median.md) / [`percentileBy`](percentile.md) – to get the row with the value closest to the estimated 
+* [`medianBy`](median.md) / [`percentileBy`](percentile.md) – to get the row at the position closest to the estimated 
 median/percentile index of the [`row expression`](DataRow.md#row-expressions)'s results calculated on rows within each group.
 
 These functions return an instance of `ReducedGroupBy`, which is a class serving as a transitional step

docs/StardustDocs/topics/pivot.md

@@ -219,8 +219,10 @@ Reducing is a specific case of [`aggregation`](pivot.md#aggregation).
 ### Step 1: use a reducing method
 Use the following functions to collapse each group in a [`Pivot`](pivot.md) into a single row:
 * [`first`](first.md) / [`last`](last.md) — take the first or last row (optionally, the first or last one that satisfies a predicate) of each group;
-* [`minBy`](minBy.md) / [`maxBy`](maxBy.md) — take the row with the minimum or maximum value of the given `RowExpression` evaluated on rows within each group;
-* [`medianBy`](median.md) / [`percentileBy`](percentile.md) — take the row with the median or a specific percentile value of the given `RowExpression` evaluated on rows within each group.
+* [`minBy`](minBy.md) / [`maxBy`](maxBy.md) — take the row with the minimum or maximum value 
+of the given [`row expression`](DataRow.md#row-expressions) evaluated on rows within each group;
+* [`medianBy`](median.md) / [`percentileBy`](percentile.md) — take the row at the position closest to the estimated
+median/percentile index of the [`row expression`](DataRow.md#row-expressions)'s results calculated on rows within each group.
 
 These functions return an instance of `ReducedPivot`, which is a class serving as a transitional step between performing a reduction on [`Pivot`](pivot.md) groups 
 and specifying how the resulting reduced rows should be represented in a resulting [`DataRow`](DataRow.md).