Add missing aggregate functions

AGENTS.md

@@ -42,3 +42,15 @@ Every Python function must include a docstring with usage examples.
 - **Alias functions**: Functions that are simple aliases (e.g., `list_sort` aliasing
   `array_sort`) only need a one-line description and a `See Also` reference to the
   primary function. They do not need their own examples.
+
+## Aggregate and Window Function Documentation
+
+When adding or updating an aggregate or window function, ensure the corresponding
+site documentation is kept in sync:
+
+- **Aggregations**: `docs/source/user-guide/common-operations/aggregations.rst` —
+  add new aggregate functions to the "Aggregate Functions" list and include usage
+  examples if appropriate.
+- **Window functions**: `docs/source/user-guide/common-operations/windows.rst` —
+  add new window functions to the "Available Functions" list and include usage
+  examples if appropriate.

crates/core/src/expr/grouping_set.rs

@@ -15,9 +15,11 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use datafusion::logical_expr::GroupingSet;
+use datafusion::logical_expr::{Expr, GroupingSet};
 use pyo3::prelude::*;
 
+use crate::expr::PyExpr;
+
 #[pyclass(
     from_py_object,
     frozen,
@@ -30,6 +32,39 @@ pub struct PyGroupingSet {
     grouping_set: GroupingSet,
 }
 
+#[pymethods]
+impl PyGroupingSet {
+    #[staticmethod]
+    #[pyo3(signature = (*exprs))]
+    fn rollup(exprs: Vec<PyExpr>) -> PyExpr {
+        Expr::GroupingSet(GroupingSet::Rollup(
+            exprs.into_iter().map(|e| e.expr).collect(),
+        ))
+        .into()
+    }
+
+    #[staticmethod]
+    #[pyo3(signature = (*exprs))]
+    fn cube(exprs: Vec<PyExpr>) -> PyExpr {
+        Expr::GroupingSet(GroupingSet::Cube(
+            exprs.into_iter().map(|e| e.expr).collect(),
+        ))
+        .into()
+    }
+
+    #[staticmethod]
+    #[pyo3(signature = (*expr_lists))]
+    fn grouping_sets(expr_lists: Vec<Vec<PyExpr>>) -> PyExpr {
+        Expr::GroupingSet(GroupingSet::GroupingSets(
+            expr_lists
+                .into_iter()
+                .map(|list| list.into_iter().map(|e| e.expr).collect())
+                .collect(),
+        ))
+        .into()
+    }
+}
+
 impl From<PyGroupingSet> for GroupingSet {
     fn from(grouping_set: PyGroupingSet) -> Self {
         grouping_set.grouping_set

crates/core/src/functions.rs

@@ -791,9 +791,10 @@ aggregate_function!(var_pop);
 aggregate_function!(approx_distinct);
 aggregate_function!(approx_median);
 
-// Code is commented out since grouping is not yet implemented
-// https://github.com/apache/datafusion-python/issues/861
-// aggregate_function!(grouping);
+// The grouping function's physical plan is not implemented, but the
+// ResolveGroupingFunction analyzer rule rewrites it before the physical
+// planner sees it, so it works correctly at runtime.
+aggregate_function!(grouping);
 
 #[pyfunction]
 #[pyo3(signature = (sort_expression, percentile, num_centroids=None, filter=None))]
@@ -831,6 +832,19 @@ pub fn approx_percentile_cont_with_weight(
     add_builder_fns_to_aggregate(agg_fn, None, filter, None, None)
 }
 
+#[pyfunction]
+#[pyo3(signature = (sort_expression, percentile, filter=None))]
+pub fn percentile_cont(
+    sort_expression: PySortExpr,
+    percentile: f64,
+    filter: Option<PyExpr>,
+) -> PyDataFusionResult<PyExpr> {
+    let agg_fn =
+        functions_aggregate::expr_fn::percentile_cont(sort_expression.sort, lit(percentile));
+
+    add_builder_fns_to_aggregate(agg_fn, None, filter, None, None)
+}
+
 // We handle last_value explicitly because the signature expects an order_by
 // https://github.com/apache/datafusion/issues/12376
 #[pyfunction]
@@ -1031,6 +1045,7 @@ pub(crate) fn init_module(m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_wrapped(wrap_pyfunction!(approx_median))?;
     m.add_wrapped(wrap_pyfunction!(approx_percentile_cont))?;
     m.add_wrapped(wrap_pyfunction!(approx_percentile_cont_with_weight))?;
+    m.add_wrapped(wrap_pyfunction!(percentile_cont))?;
     m.add_wrapped(wrap_pyfunction!(range))?;
     m.add_wrapped(wrap_pyfunction!(array_agg))?;
     m.add_wrapped(wrap_pyfunction!(arrow_typeof))?;
@@ -1080,7 +1095,7 @@ pub(crate) fn init_module(m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_wrapped(wrap_pyfunction!(from_unixtime))?;
     m.add_wrapped(wrap_pyfunction!(gcd))?;
     m.add_wrapped(wrap_pyfunction!(greatest))?;
-    // m.add_wrapped(wrap_pyfunction!(grouping))?;
+    m.add_wrapped(wrap_pyfunction!(grouping))?;
     m.add_wrapped(wrap_pyfunction!(in_list))?;
     m.add_wrapped(wrap_pyfunction!(initcap))?;
     m.add_wrapped(wrap_pyfunction!(isnan))?;

docs/source/user-guide/common-operations/aggregations.rst

@@ -163,6 +163,168 @@ Suppose we want to find the speed values for only Pokemon that have low Attack v
         f.avg(col_speed, filter=col_attack < lit(50)).alias("Avg Speed Low Attack")])
 
 
+Grouping Sets
+-------------
+
+The default style of aggregation produces one row per group. Sometimes you want a single query to
+produce rows at multiple levels of detail — for example, totals per type *and* an overall grand
+total, or subtotals for every combination of two columns plus the individual column totals. Writing
+separate queries and concatenating them is tedious and runs the data multiple times. Grouping sets
+solve this by letting you specify several grouping levels in one pass.
+
+DataFusion supports three grouping set styles through the
+:py:class:`~datafusion.expr.GroupingSet` class:
+
+- :py:meth:`~datafusion.expr.GroupingSet.rollup` — hierarchical subtotals, like a drill-down report
+- :py:meth:`~datafusion.expr.GroupingSet.cube` — every possible subtotal combination, like a pivot table
+- :py:meth:`~datafusion.expr.GroupingSet.grouping_sets` — explicitly list exactly which grouping levels you want
+
+Because result rows come from different grouping levels, a column that is *not* part of a
+particular level will be ``null`` in that row. Use :py:func:`~datafusion.functions.grouping` to
+distinguish a real ``null`` in the data from one that means "this column was aggregated across."
+It returns ``0`` when the column is a grouping key for that row, and ``1`` when it is not.
+
+Rollup
+^^^^^^
+
+:py:meth:`~datafusion.expr.GroupingSet.rollup` creates a hierarchy. ``rollup(a, b)`` produces
+grouping sets ``(a, b)``, ``(a)``, and ``()`` — like nested subtotals in a report. This is useful
+when your columns have a natural hierarchy, such as region → city or type → subtype.
+
+Suppose we want to summarize Pokemon stats by ``Type 1`` with subtotals and a grand total. With
+the default aggregation style we would need two separate queries. With ``rollup`` we get it all at
+once:
+
+.. ipython:: python
+
+    from datafusion.expr import GroupingSet
+
+    df.aggregate(
+        [GroupingSet.rollup(col_type_1)],
+        [f.count(col_speed).alias("Count"),
+         f.avg(col_speed).alias("Avg Speed"),
+         f.max(col_speed).alias("Max Speed")]
+    ).sort(col_type_1.sort(ascending=True, nulls_first=True))
+
+The first row — where ``Type 1`` is ``null`` — is the grand total across all types. But how do you
+tell a grand-total ``null`` apart from a Pokemon that genuinely has no type? The
+:py:func:`~datafusion.functions.grouping` function returns ``0`` when the column is a grouping key
+for that row and ``1`` when it is aggregated across.
+
+.. note::
+
+    Due to an upstream DataFusion limitation
+    (`apache/datafusion#21411 <https://github.com/apache/datafusion/issues/21411>`_),
+    ``.alias()`` cannot be applied directly to a ``grouping()`` expression — it will raise an
+    error at execution time. Instead, use
+    :py:meth:`~datafusion.dataframe.DataFrame.with_column_renamed` on the result DataFrame to
+    give the column a readable name. Once the upstream issue is resolved, you will be able to
+    use ``.alias()`` directly and the workaround below will no longer be necessary.
+
+The raw column name generated by ``grouping()`` contains internal identifiers, so we use
+:py:meth:`~datafusion.dataframe.DataFrame.with_column_renamed` to clean it up:
+
+.. ipython:: python
+
+    result = df.aggregate(
+        [GroupingSet.rollup(col_type_1)],
+        [f.count(col_speed).alias("Count"),
+         f.avg(col_speed).alias("Avg Speed"),
+         f.grouping(col_type_1)]
+    )
+    for field in result.schema():
+        if field.name.startswith("grouping("):
+            result = result.with_column_renamed(field.name, "Is Total")
+    result.sort(col_type_1.sort(ascending=True, nulls_first=True))
+
+With two columns the hierarchy becomes more apparent. ``rollup(Type 1, Type 2)`` produces:
+
+- one row per ``(Type 1, Type 2)`` pair — the most detailed level
+- one row per ``Type 1`` — subtotals
+- one grand total row
+
+.. ipython:: python
+
+    df.aggregate(
+        [GroupingSet.rollup(col_type_1, col_type_2)],
+        [f.count(col_speed).alias("Count"),
+         f.avg(col_speed).alias("Avg Speed")]
+    ).sort(
+        col_type_1.sort(ascending=True, nulls_first=True),
+        col_type_2.sort(ascending=True, nulls_first=True)
+    )
+
+Cube
+^^^^
+
+:py:meth:`~datafusion.expr.GroupingSet.cube` produces every possible subset. ``cube(a, b)``
+produces grouping sets ``(a, b)``, ``(a)``, ``(b)``, and ``()`` — one more than ``rollup`` because
+it also includes ``(b)`` alone. This is useful when neither column is "above" the other in a
+hierarchy and you want all cross-tabulations.
+
+For our Pokemon data, ``cube(Type 1, Type 2)`` gives us stats broken down by the type pair,
+by ``Type 1`` alone, by ``Type 2`` alone, and a grand total — all in one query:
+
+.. ipython:: python
+
+    df.aggregate(
+        [GroupingSet.cube(col_type_1, col_type_2)],
+        [f.count(col_speed).alias("Count"),
+         f.avg(col_speed).alias("Avg Speed")]
+    ).sort(
+        col_type_1.sort(ascending=True, nulls_first=True),
+        col_type_2.sort(ascending=True, nulls_first=True)
+    )
+
+Compared to the ``rollup`` example above, notice the extra rows where ``Type 1`` is ``null`` but
+``Type 2`` has a value — those are the per-``Type 2`` subtotals that ``rollup`` does not include.
+
+Explicit Grouping Sets
+^^^^^^^^^^^^^^^^^^^^^^
+
+:py:meth:`~datafusion.expr.GroupingSet.grouping_sets` lets you list exactly which grouping levels
+you need when ``rollup`` or ``cube`` would produce too many or too few. Each argument is a list of
+columns forming one grouping set.
+
+For example, if we want only the per-``Type 1`` totals and per-``Type 2`` totals — but *not* the
+full ``(Type 1, Type 2)`` detail rows or the grand total — we can ask for exactly that:
+
+.. ipython:: python
+
+    df.aggregate(
+        [GroupingSet.grouping_sets([col_type_1], [col_type_2])],
+        [f.count(col_speed).alias("Count"),
+         f.avg(col_speed).alias("Avg Speed")]
+    ).sort(
+        col_type_1.sort(ascending=True, nulls_first=True),
+        col_type_2.sort(ascending=True, nulls_first=True)
+    )
+
+Each row belongs to exactly one grouping level. The :py:func:`~datafusion.functions.grouping`
+function tells you which level each row comes from:
+
+.. ipython:: python
+
+    result = df.aggregate(
+        [GroupingSet.grouping_sets([col_type_1], [col_type_2])],
+        [f.count(col_speed).alias("Count"),
+         f.avg(col_speed).alias("Avg Speed"),
+         f.grouping(col_type_1),
+         f.grouping(col_type_2)]
+    )
+    for field in result.schema():
+        if field.name.startswith("grouping("):
+            clean = field.name.split(".")[-1].rstrip(")")
+            result = result.with_column_renamed(field.name, f"grouping({clean})")
+    result.sort(
+        col_type_1.sort(ascending=True, nulls_first=True),
+        col_type_2.sort(ascending=True, nulls_first=True)
+    )
+
+Where ``grouping(Type 1)`` is ``0`` the row is a per-``Type 1`` total (and ``Type 2`` is ``null``).
+Where ``grouping(Type 2)`` is ``0`` the row is a per-``Type 2`` total (and ``Type 1`` is ``null``).
+
+
 Aggregate Functions
 -------------------
 
@@ -192,6 +354,7 @@ The available aggregate functions are:
     - :py:func:`datafusion.functions.stddev_pop`
     - :py:func:`datafusion.functions.var_samp`
     - :py:func:`datafusion.functions.var_pop`
+    - :py:func:`datafusion.functions.var_population`
 6. Linear Regression Functions
     - :py:func:`datafusion.functions.regr_count`
     - :py:func:`datafusion.functions.regr_slope`
@@ -208,9 +371,16 @@ The available aggregate functions are:
     - :py:func:`datafusion.functions.nth_value`
 8. String Functions
     - :py:func:`datafusion.functions.string_agg`
-9. Approximation Functions
+9. Percentile Functions
+    - :py:func:`datafusion.functions.percentile_cont`
+    - :py:func:`datafusion.functions.quantile_cont`
     - :py:func:`datafusion.functions.approx_distinct`
     - :py:func:`datafusion.functions.approx_median`
     - :py:func:`datafusion.functions.approx_percentile_cont`
     - :py:func:`datafusion.functions.approx_percentile_cont_with_weight`
+10. Grouping Set Functions
+    - :py:func:`datafusion.functions.grouping`
+    - :py:meth:`datafusion.expr.GroupingSet.rollup`
+    - :py:meth:`datafusion.expr.GroupingSet.cube`
+    - :py:meth:`datafusion.expr.GroupingSet.grouping_sets`
 

python/datafusion/dataframe.py

@@ -633,8 +633,22 @@ def aggregate(
     ) -> DataFrame:
         """Aggregates the rows of the current DataFrame.
 
+        By default each unique combination of the ``group_by`` columns
+        produces one row. To get multiple levels of subtotals in a
+        single pass, pass a
+        :py:class:`~datafusion.expr.GroupingSet` expression
+        (created via
+        :py:meth:`~datafusion.expr.GroupingSet.rollup`,
+        :py:meth:`~datafusion.expr.GroupingSet.cube`, or
+        :py:meth:`~datafusion.expr.GroupingSet.grouping_sets`)
+        as the ``group_by`` argument.  See the
+        :ref:`aggregation` user guide for detailed examples.
+
         Args:
-            group_by: Sequence of expressions or column names to group by.
+            group_by: Sequence of expressions or column names to group
+                by. A :py:class:`~datafusion.expr.GroupingSet`
+                expression may be included to produce multiple grouping
+                levels (rollup, cube, or explicit grouping sets).
             aggs: Sequence of expressions to aggregate.
 
         Returns: