chore: Consolidate Example: simplify_udwf_expression.rs into advanced_udwf.rs

datafusion-examples/examples/advanced_udwf.rs

@@ -24,11 +24,14 @@ use arrow::{
 };
 use arrow_schema::Field;
 use datafusion::error::Result;
+use datafusion::functions_aggregate::average::avg_udaf;
 use datafusion::prelude::*;
 use datafusion_common::ScalarValue;
-use datafusion_expr::function::WindowUDFFieldArgs;
+use datafusion_expr::expr::WindowFunction;
+use datafusion_expr::function::{WindowFunctionSimplification, WindowUDFFieldArgs};
+use datafusion_expr::simplify::SimplifyInfo;
 use datafusion_expr::{
-    PartitionEvaluator, Signature, WindowFrame, WindowUDF, WindowUDFImpl,
+    Expr, PartitionEvaluator, Signature, WindowFrame, WindowUDF, WindowUDFImpl,
 };
 use datafusion_functions_window_common::partition::PartitionEvaluatorArgs;
 
@@ -142,6 +145,67 @@ impl PartitionEvaluator for MyPartitionEvaluator {
     }
 }
 
+/// This UDWF will show how to use the WindowUDFImpl::simplify() API
+#[derive(Debug, Clone)]
+struct SimplifySmoothItUdf {
+    signature: Signature,
+}
+
+impl SimplifySmoothItUdf {
+    fn new() -> Self {
+        Self {
+            signature: Signature::exact(
+                // this function will always take one arguments of type f64
+                vec![DataType::Float64],
+                // this function is deterministic and will always return the same
+                // result for the same input
+                Volatility::Immutable,
+            ),
+        }
+    }
+}
+impl WindowUDFImpl for SimplifySmoothItUdf {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "simplify_smooth_it"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn partition_evaluator(
+        &self,
+        _partition_evaluator_args: PartitionEvaluatorArgs,
+    ) -> Result<Box<dyn PartitionEvaluator>> {
+        todo!()
+    }
+
+    /// this function will simplify `SimplifySmoothItUdf` to `AggregateUDF` for `Avg`
+    /// default implementation will not be called (left as `todo!()`)
+    fn simplify(&self) -> Option<WindowFunctionSimplification> {
+        let simplify = |window_function: WindowFunction, _: &dyn SimplifyInfo| {
+            Ok(Expr::WindowFunction(WindowFunction {
+                fun: datafusion_expr::WindowFunctionDefinition::AggregateUDF(avg_udaf()),
+                args: window_function.args,
+                partition_by: window_function.partition_by,
+                order_by: window_function.order_by,
+                window_frame: window_function.window_frame,
+                null_treatment: window_function.null_treatment,
+            }))
+        };
+
+        Some(Box::new(simplify))
+    }
+
+    fn field(&self, field_args: WindowUDFFieldArgs) -> Result<Field> {
+        Ok(Field::new(field_args.name(), DataType::Float64, true))
+    }
+}
+
 // create local execution context with `cars.csv` registered as a table named `cars`
 async fn create_context() -> Result<SessionContext> {
     // declare a new context. In spark API, this corresponds to a new spark SQL session
@@ -162,12 +226,15 @@ async fn main() -> Result<()> {
     let smooth_it = WindowUDF::from(SmoothItUdf::new());
     ctx.register_udwf(smooth_it.clone());
 
-    // Use SQL to run the new window function
+    let simplify_smooth_it = WindowUDF::from(SimplifySmoothItUdf::new());
+    ctx.register_udwf(simplify_smooth_it.clone());
+
+    // Use SQL to retrieve entire table
     let df = ctx.sql("SELECT * from cars").await?;
     // print the results
     df.show().await?;
 
-    // Use SQL to run the new window function:
+    // Use SQL to run smooth_it:
     //
     // `PARTITION BY car`:each distinct value of car (red, and green)
     // should be treated as a separate partition (and will result in
@@ -201,7 +268,7 @@ async fn main() -> Result<()> {
     // print the results
     df.show().await?;
 
-    // this time, call the new widow function with an explicit
+    // this time, call the function with an explicit
     // window so evaluate will be invoked with each window.
     //
     // `ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING`: each invocation
@@ -232,5 +299,22 @@ async fn main() -> Result<()> {
     // print the results
     df.show().await?;
 
+    // Use SQL to run simplify_smooth_it
+    let df = ctx
+        .sql(
+            "SELECT \
+               car, \
+               speed, \
+               simplify_smooth_it(speed) OVER (PARTITION BY car ORDER BY time) AS smooth_speed,\
+               time \
+               from cars \
+             ORDER BY \
+               car",
+        )
+        .await?;
+
+    // print the results
+    df.show().await?;
+
     Ok(())
 }

datafusion/expr/src/udwf.rs

@@ -344,7 +344,7 @@ pub trait WindowUDFImpl: Debug + Send + Sync {
     /// optimizations manually for specific UDFs.
     ///
     /// Example:
-    /// [`simplify_udwf_expression.rs`]: <https://github.com/apache/arrow-datafusion/blob/main/datafusion-examples/examples/simplify_udwf_expression.rs>
+    /// [`advanced_udwf.rs`]: <https://github.com/apache/arrow-datafusion/blob/main/datafusion-examples/examples/advanced_udwf.rs>
     ///
     /// # Returns
     /// [None] if simplify is not defined or,