[REVIEW] Add support for LEAD/LAG window functions for fixed-width types [redux]

CHANGELOG.md

@@ -17,6 +17,7 @@
 - PR #6271 Add support to deep-copy struct columns from struct column-view
 - PR #6254 Add `cudf::make_dictionary_from_scalar` factory function
 - PR #6262 Add nth_element series aggregation with null handling
+- PR #6277 Add support for LEAD/LAG window functions for fixed-width types
 - PR #6302 Add custom dataframe accessors
 - PR #6301 Add JNI bindings to nvcomp
 

cpp/include/cudf/aggregation.hpp

@@ -71,6 +71,8 @@ class aggregation {
     NTH_ELEMENT,     ///< get the nth element
     ROW_NUMBER,      ///< get row-number of element
     COLLECT,         ///< collect values into a list
+    LEAD,            ///< window function, accesses row at specified offset following current row
+    LAG,             ///< window function, accesses row at specified offset preceding current row
     PTX,             ///< PTX UDF based reduction
     CUDA             ///< CUDA UDf based reduction
   };
@@ -197,6 +199,12 @@ std::unique_ptr<aggregation> make_row_number_aggregation();
 /// Factory to create a COLLECT_NUMBER aggregation
 std::unique_ptr<aggregation> make_collect_aggregation();
 
+/// Factory to create a LAG aggregation
+std::unique_ptr<aggregation> make_lag_aggregation(size_type offset);
+
+/// Factory to create a LEAD aggregation
+std::unique_ptr<aggregation> make_lead_aggregation(size_type offset);
+
 /**
  * @brief Factory to create an aggregation base on UDF for PTX or CUDA
  *

cpp/include/cudf/detail/aggregation/aggregation.hpp

@@ -92,6 +92,23 @@ struct quantile_aggregation final : derived_aggregation<quantile_aggregation> {
   }
 };
 
+struct lead_lag_aggregation final : derived_aggregation<lead_lag_aggregation> {
+  lead_lag_aggregation(Kind kind, size_type offset)
+    : derived_aggregation{offset < 0 ? (kind == LAG ? LEAD : LAG) : kind},
+      row_offset{std::abs(offset)}
+  {
+  }
+
+  size_type row_offset;
+
+ protected:
+  friend class derived_aggregation<lead_lag_aggregation>;
+
+  bool operator==(lead_lag_aggregation const& rhs) const { return row_offset == rhs.row_offset; }
+
+  size_t hash_impl() const { return std::hash<size_type>()(row_offset); }
+};
+
 /**
  * @brief Derived class for specifying a standard deviation/variance aggregation
  */
@@ -361,6 +378,18 @@ struct target_type_impl<Source, aggregation::COLLECT> {
   using type = cudf::list_view;
 };
 
+// Always use Source for LEAD
+template <typename Source>
+struct target_type_impl<Source, aggregation::LEAD> {
+  using type = Source;
+};
+
+// Always use Source for LAG
+template <typename Source>
+struct target_type_impl<Source, aggregation::LAG> {
+  using type = Source;
+};
+
 /**
  * @brief Helper alias to get the accumulator type for performing aggregation
  * `k` on elements of type `Source`
@@ -448,6 +477,10 @@ CUDA_HOST_DEVICE_CALLABLE decltype(auto) aggregation_dispatcher(aggregation::Kin
       return f.template operator()<aggregation::ROW_NUMBER>(std::forward<Ts>(args)...);
     case aggregation::COLLECT:
       return f.template operator()<aggregation::COLLECT>(std::forward<Ts>(args)...);
+    case aggregation::LEAD:
+      return f.template operator()<aggregation::LEAD>(std::forward<Ts>(args)...);
+    case aggregation::LAG:
+      return f.template operator()<aggregation::LAG>(std::forward<Ts>(args)...);
     default: {
 #ifndef __CUDA_ARCH__
       CUDF_FAIL("Unsupported aggregation.");

cpp/include/cudf/detail/utilities/device_operators.cuh

@@ -222,6 +222,15 @@ struct DeviceXor {
   }
 };
 
+/**
+ * @brief Operator for calculating Lead/Lag window function.
+ */
+struct DeviceLeadLag {
+  const size_type row_offset;
+
+  explicit CUDA_HOST_DEVICE_CALLABLE DeviceLeadLag(size_type offset_) : row_offset(offset_) {}
+};
+
 }  // namespace cudf
 
 #endif

cpp/include/cudf/rolling.hpp

@@ -61,6 +61,28 @@ std::unique_ptr<column> rolling_window(
   std::unique_ptr<aggregation> const& agg,
   rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 
+/**
+ * @copydoc std::unique_ptr<column> rolling_window(
+ *            column_view const& input,
+ *            size_type preceding_window,
+ *            size_type following_window,
+ *            size_type min_periods,
+ *            std::unique_ptr<aggregation> const& agg,
+ *            rmm::mr::device_memory_resource* mr)
+ *
+ * @param default_outputs A column of per-row default values to be returned instead
+ *                        of nulls. Used for LEAD()/LAG(), if the row offset crosses
+ *                        the boundaries of the column.
+ */
+std::unique_ptr<column> rolling_window(
+  column_view const& input,
+  column_view const& default_outputs,
+  size_type preceding_window,
+  size_type following_window,
+  size_type min_periods,
+  std::unique_ptr<aggregation> const& agg,
+  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
 /**
  * @brief  Applies a grouping-aware, fixed-size rolling window function to the values in a column.
  *
@@ -140,6 +162,30 @@ std::unique_ptr<column> grouped_rolling_window(
   std::unique_ptr<aggregation> const& aggr,
   rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 
+/**
+ * @copydoc std::unique_ptr<column> grouped_rolling_window(
+ *            table_view const& group_keys,
+ *            column_view const& input,
+ *            size_type preceding_window,
+ *            size_type following_window,
+ *            size_type min_periods,
+ *            std::unique_ptr<aggregation> const& aggr,
+ *            rmm::mr::device_memory_resource* mr)
+ *
+ * @param default_outputs A column of per-row default values to be returned instead
+ *                        of nulls. Used for LEAD()/LAG(), if the row offset crosses
+ *                        the boundaries of the column or group.
+ */
+std::unique_ptr<column> grouped_rolling_window(
+  table_view const& group_keys,
+  column_view const& input,
+  column_view const& default_outputs,
+  size_type preceding_window,
+  size_type following_window,
+  size_type min_periods,
+  std::unique_ptr<aggregation> const& aggr,
+  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
 /**
  * @brief  Applies a grouping-aware, timestamp-based rolling window function to the values in a
  *column.

cpp/src/aggregation/aggregation.cpp

@@ -121,6 +121,16 @@ std::unique_ptr<aggregation> make_collect_aggregation()
 {
   return std::make_unique<aggregation>(aggregation::COLLECT);
 }
+/// Factory to create a LAG aggregation
+std::unique_ptr<aggregation> make_lag_aggregation(size_type offset)
+{
+  return std::make_unique<cudf::detail::lead_lag_aggregation>(aggregation::LAG, offset);
+}
+/// Factory to create a LEAD aggregation
+std::unique_ptr<aggregation> make_lead_aggregation(size_type offset)
+{
+  return std::make_unique<cudf::detail::lead_lag_aggregation>(aggregation::LEAD, offset);
+}
 /// Factory to create a UDF aggregation
 std::unique_ptr<aggregation> make_udf_aggregation(udf_type type,
                                                   std::string const& user_defined_aggregator,