Migrate documentation for Aggregate Functions to code (#12861)

* aggregate function migration

* fmt fix

Author: jonathanc-n

datafusion/functions-aggregate/src/approx_distinct.rs

@@ -31,13 +31,17 @@ use datafusion_common::ScalarValue;
 use datafusion_common::{
     downcast_value, internal_err, not_impl_err, DataFusionError, Result,
 };
+use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::utils::format_state_name;
-use datafusion_expr::{Accumulator, AggregateUDFImpl, Signature, Volatility};
+use datafusion_expr::{
+    Accumulator, AggregateUDFImpl, Documentation, Signature, Volatility,
+};
 use std::any::Any;
 use std::fmt::{Debug, Formatter};
 use std::hash::Hash;
 use std::marker::PhantomData;
+use std::sync::OnceLock;
 make_udaf_expr_and_func!(
     ApproxDistinct,
     approx_distinct,
@@ -303,4 +307,33 @@ impl AggregateUDFImpl for ApproxDistinct {
         };
         Ok(accumulator)
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_approx_distinct_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_approx_distinct_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_APPROXIMATE)
+            .with_description(
+                "Returns the approximate number of distinct input values calculated using the HyperLogLog algorithm.",
+            )
+            .with_syntax_example("approx_distinct(expression)")
+            .with_sql_example(r#"```sql
+> SELECT approx_distinct(column_name) FROM table_name;
++-----------------------------------+
+| approx_distinct(column_name)      |
++-----------------------------------+
+| 42                                |
++-----------------------------------+
+```"#, 
+            )
+            .with_argument("expression", "Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .build()
+            .unwrap()
+    })
 }

datafusion/functions-aggregate/src/approx_median.rs

@@ -19,15 +19,19 @@
 
 use std::any::Any;
 use std::fmt::Debug;
+use std::sync::OnceLock;
 
 use arrow::{datatypes::DataType, datatypes::Field};
 use arrow_schema::DataType::{Float64, UInt64};
 
 use datafusion_common::{not_impl_err, plan_err, Result};
+use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::type_coercion::aggregates::NUMERICS;
 use datafusion_expr::utils::format_state_name;
-use datafusion_expr::{Accumulator, AggregateUDFImpl, Signature, Volatility};
+use datafusion_expr::{
+    Accumulator, AggregateUDFImpl, Documentation, Signature, Volatility,
+};
 
 use crate::approx_percentile_cont::ApproxPercentileAccumulator;
 
@@ -116,4 +120,33 @@ impl AggregateUDFImpl for ApproxMedian {
             acc_args.exprs[0].data_type(acc_args.schema)?,
         )))
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_approx_median_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_approx_median_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_APPROXIMATE)
+            .with_description(
+                "Returns the approximate median (50th percentile) of input values. It is an alias of `approx_percentile_cont(x, 0.5)`.",
+            )
+            .with_syntax_example("approx_median(expression)")
+            .with_sql_example(r#"```sql
+> SELECT approx_median(column_name) FROM table_name;
++-----------------------------------+
+| approx_median(column_name)        |
++-----------------------------------+
+| 23.5                              |
++-----------------------------------+
+```"#,
+            )
+            .with_argument("expression", "Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .build()
+            .unwrap()
+    })
 }

datafusion/functions-aggregate/src/approx_percentile_cont.rs

@@ -17,7 +17,7 @@
 
 use std::any::Any;
 use std::fmt::{Debug, Formatter};
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 use arrow::array::{Array, RecordBatch};
 use arrow::compute::{filter, is_not_null};
@@ -34,12 +34,13 @@ use datafusion_common::{
     downcast_value, internal_err, not_impl_datafusion_err, not_impl_err, plan_err,
     DataFusionError, Result, ScalarValue,
 };
+use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::type_coercion::aggregates::{INTEGERS, NUMERICS};
 use datafusion_expr::utils::format_state_name;
 use datafusion_expr::{
-    Accumulator, AggregateUDFImpl, ColumnarValue, Expr, Signature, TypeSignature,
-    Volatility,
+    Accumulator, AggregateUDFImpl, ColumnarValue, Documentation, Expr, Signature,
+    TypeSignature, Volatility,
 };
 use datafusion_functions_aggregate_common::tdigest::{
     TDigest, TryIntoF64, DEFAULT_MAX_SIZE,
@@ -268,6 +269,36 @@ impl AggregateUDFImpl for ApproxPercentileCont {
         }
         Ok(arg_types[0].clone())
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_approx_percentile_cont_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_approx_percentile_cont_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_APPROXIMATE)
+            .with_description(
+                "Returns the approximate percentile of input values using the t-digest algorithm.",
+            )
+            .with_syntax_example("approx_percentile_cont(expression, percentile, centroids)")
+            .with_sql_example(r#"```sql
+> SELECT approx_percentile_cont(column_name, 0.75, 100) FROM table_name;
++-------------------------------------------------+
+| approx_percentile_cont(column_name, 0.75, 100)  |
++-------------------------------------------------+
+| 65.0                                            |
++-------------------------------------------------+
+```"#)
+            .with_argument("expression", "Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .with_argument("percentile", "Percentile to compute. Must be a float value between 0 and 1 (inclusive).")
+            .with_argument("centroids", "Number of centroids to use in the t-digest algorithm. _Default is 100_. A higher number results in more accurate approximation but requires more memory.")
+            .build()
+            .unwrap()
+    })
 }
 
 #[derive(Debug)]

datafusion/functions-aggregate/src/approx_percentile_cont_with_weight.rs

@@ -17,7 +17,7 @@
 
 use std::any::Any;
 use std::fmt::{Debug, Formatter};
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 use arrow::{
     array::ArrayRef,
@@ -26,10 +26,13 @@ use arrow::{
 
 use datafusion_common::ScalarValue;
 use datafusion_common::{not_impl_err, plan_err, Result};
+use datafusion_expr::aggregate_doc_sections::DOC_SECTION_APPROXIMATE;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::type_coercion::aggregates::NUMERICS;
 use datafusion_expr::Volatility::Immutable;
-use datafusion_expr::{Accumulator, AggregateUDFImpl, Signature, TypeSignature};
+use datafusion_expr::{
+    Accumulator, AggregateUDFImpl, Documentation, Signature, TypeSignature,
+};
 use datafusion_functions_aggregate_common::tdigest::{
     Centroid, TDigest, DEFAULT_MAX_SIZE,
 };
@@ -151,6 +154,37 @@ impl AggregateUDFImpl for ApproxPercentileContWithWeight {
     fn state_fields(&self, args: StateFieldsArgs) -> Result<Vec<Field>> {
         self.approx_percentile_cont.state_fields(args)
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_approx_percentile_cont_with_weight_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_approx_percentile_cont_with_weight_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_APPROXIMATE)
+            .with_description(
+                "Returns the weighted approximate percentile of input values using the t-digest algorithm.",
+            )
+            .with_syntax_example("approx_percentile_cont_with_weight(expression, weight, percentile)")
+            .with_sql_example(r#"```sql
+> SELECT approx_percentile_cont_with_weight(column_name, weight_column, 0.90) FROM table_name;
++----------------------------------------------------------------------+
+| approx_percentile_cont_with_weight(column_name, weight_column, 0.90) |
++----------------------------------------------------------------------+
+| 78.5                                                                 |
++----------------------------------------------------------------------+
+```"#,
+            )
+            .with_argument("expression", "Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .with_argument("weight", "Expression to use as weight. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .with_argument("percentile", "Percentile to compute. Must be a float value between 0 and 1 (inclusive).")
+            .build()
+            .unwrap()
+    })
 }
 
 #[derive(Debug)]

datafusion/functions-aggregate/src/array_agg.rs

@@ -25,15 +25,16 @@ use datafusion_common::cast::as_list_array;
 use datafusion_common::utils::{array_into_list_array_nullable, get_row_at_idx};
 use datafusion_common::{exec_err, ScalarValue};
 use datafusion_common::{internal_err, Result};
+use datafusion_expr::aggregate_doc_sections::DOC_SECTION_GENERAL;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::utils::format_state_name;
-use datafusion_expr::AggregateUDFImpl;
 use datafusion_expr::{Accumulator, Signature, Volatility};
+use datafusion_expr::{AggregateUDFImpl, Documentation};
 use datafusion_functions_aggregate_common::merge_arrays::merge_ordered_arrays;
 use datafusion_functions_aggregate_common::utils::ordering_fields;
 use datafusion_physical_expr_common::sort_expr::{LexOrdering, PhysicalSortExpr};
 use std::collections::{HashSet, VecDeque};
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 make_udaf_expr_and_func!(
     ArrayAgg,
@@ -142,6 +143,35 @@ impl AggregateUDFImpl for ArrayAgg {
     fn reverse_expr(&self) -> datafusion_expr::ReversedUDAF {
         datafusion_expr::ReversedUDAF::Reversed(array_agg_udaf())
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_array_agg_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_array_agg_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_GENERAL)
+            .with_description(
+                "Returns an array created from the expression elements. If ordering is required, elements are inserted in the specified order.",
+            )
+            .with_syntax_example("array_agg(expression [ORDER BY expression])")
+            .with_sql_example(r#"```sql
+> SELECT array_agg(column_name ORDER BY other_column) FROM table_name;
++-----------------------------------------------+
+| array_agg(column_name ORDER BY other_column)  |
++-----------------------------------------------+
+| [element1, element2, element3]                |
++-----------------------------------------------+
+```"#, 
+            )
+            .with_argument("expression", "Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .build()
+            .unwrap()
+    })
 }
 
 #[derive(Debug)]

datafusion/functions-aggregate/src/average.rs

@@ -28,12 +28,14 @@ use arrow::datatypes::{
     Float64Type, UInt64Type,
 };
 use datafusion_common::{exec_err, not_impl_err, Result, ScalarValue};
+use datafusion_expr::aggregate_doc_sections::DOC_SECTION_GENERAL;
 use datafusion_expr::function::{AccumulatorArgs, StateFieldsArgs};
 use datafusion_expr::type_coercion::aggregates::{avg_return_type, coerce_avg_type};
 use datafusion_expr::utils::format_state_name;
 use datafusion_expr::Volatility::Immutable;
 use datafusion_expr::{
-    Accumulator, AggregateUDFImpl, EmitTo, GroupsAccumulator, ReversedUDAF, Signature,
+    Accumulator, AggregateUDFImpl, Documentation, EmitTo, GroupsAccumulator,
+    ReversedUDAF, Signature,
 };
 
 use datafusion_functions_aggregate_common::aggregate::groups_accumulator::accumulate::NullState;
@@ -45,7 +47,7 @@ use datafusion_functions_aggregate_common::utils::DecimalAverager;
 use log::debug;
 use std::any::Any;
 use std::fmt::Debug;
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 make_udaf_expr_and_func!(
     Avg,
@@ -235,6 +237,36 @@ impl AggregateUDFImpl for Avg {
         }
         coerce_avg_type(self.name(), arg_types)
     }
+
+    fn documentation(&self) -> Option<&Documentation> {
+        Some(get_avg_doc())
+    }
+}
+
+static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();
+
+fn get_avg_doc() -> &'static Documentation {
+    DOCUMENTATION.get_or_init(|| {
+        Documentation::builder()
+            .with_doc_section(DOC_SECTION_GENERAL)
+            .with_description(
+                "Returns the average of numeric values in the specified column.",
+            )
+            .with_syntax_example("avg(expression)")
+            .with_sql_example(r#"```sql
+> SELECT avg(column_name) FROM table_name;
++---------------------------+
+| avg(column_name)           |
++---------------------------+
+| 42.75                      |
++---------------------------+
+```"#, 
+            )
+            .with_argument("expression", "Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.")
+            .with_argument("Aliases: ", "`mean`")
+            .build()
+            .unwrap()
+    })
 }
 
 /// An accumulator to compute the average