alamb commented on code in PR #8719:
URL: https://github.com/apache/arrow-datafusion/pull/8719#discussion_r1439922333
##########
datafusion/expr/src/udwf.rs:
##########
@@ -140,3 +171,86 @@ impl WindowUDF {
(self.partition_evaluator_factory)()
}
}
+
+impl<F> From<F> for WindowUDF
+where
+ F: WindowUDFImpl + Send + Sync + 'static,
+{
+ fn from(fun: F) -> Self {
+ Self::new_from_impl(fun)
+ }
+}
+
+/// Trait for implementing [`WindowUDF`].
+///
+/// This trait exposes the full API for implementing user defined window
functions and
+/// can be used to implement any function.
+///
+/// See [`advanced_udwf.rs`] for a full example with complete implementation
and
+/// [`WindowUDF`] for other available options.
+///
+///
+/// [`advanced_udwf.rs`]:
https://github.com/apache/arrow-datafusion/blob/main/datafusion-examples/examples/advanced_udwf.rs
+/// # Basic Example
+/// ```
+/// # use std::any::Any;
+/// # use arrow::datatypes::DataType;
+/// # use datafusion_common::{DataFusionError, plan_err, Result};
+/// # use datafusion_expr::{col, Signature, Volatility, PartitionEvaluator,
WindowFrame};
+/// # use datafusion_expr::{WindowUDFImpl, WindowUDF};
+/// struct SmoothIt {
+/// signature: Signature
+/// };
+///
+/// impl SmoothIt {
+/// fn new() -> Self {
+/// Self {
+/// signature: Signature::uniform(1, vec![DataType::Int32],
Volatility::Immutable)
+/// }
+/// }
+/// }
+///
+/// /// Implement the WindowUDFImpl trait for AddOne
+/// impl WindowUDFImpl for SmoothIt {
+/// fn as_any(&self) -> &dyn Any { self }
+/// fn name(&self) -> &str { "smooth_it" }
+/// fn signature(&self) -> &Signature { &self.signature }
+/// fn return_type(&self, args: &[DataType]) -> Result<DataType> {
+/// if !matches!(args.get(0), Some(&DataType::Int32)) {
+/// return plan_err!("smooth_it only accepts Int32 arguments");
+/// }
+/// Ok(DataType::Int32)
+/// }
+/// // The actual implementation would add one to the argument
+/// fn invoke(&self) -> Result<Box<dyn PartitionEvaluator>> {
unimplemented!() }
+/// }
+///
+/// // Create a new ScalarUDF from the implementation
+/// let smooth_it = WindowUDF::from(SmoothIt::new());
+///
+/// // Call the function `add_one(col)`
+/// let expr = smooth_it.call(
+/// vec![col("speed")], // smooth_it(speed)
+/// vec![col("car")], // PARTITION BY car
+/// vec![col("time").sort(true, true)], // ORDER BY time ASC
+/// WindowFrame::new(false),
+/// );
+/// ```
+pub trait WindowUDFImpl {
+ /// Returns this object as an [`Any`] trait object
+ fn as_any(&self) -> &dyn Any;
+
+ /// Returns this function's name
+ fn name(&self) -> &str;
+
+ /// Returns the function's [`Signature`] for information about what input
+ /// types are accepted and the function's Volatility.
+ fn signature(&self) -> &Signature;
+
+ /// What [`DataType`] will be returned by this function, given the types of
+ /// the arguments
+ fn return_type(&self, arg_types: &[DataType]) -> Result<DataType>;
+
+ /// Invoke the function, returning the [`PartitionEvaluator`] instance
+ fn invoke(&self) -> Result<Box<dyn PartitionEvaluator>>;
Review Comment:
Would it be possible to rename this function to `partition_evaluator` as it
isn't really being invoked?
```suggestion
fn partition_evaluator(&self) -> Result<Box<dyn PartitionEvaluator>>;
```
##########
datafusion-examples/examples/advanced_udwf.rs:
##########
@@ -0,0 +1,230 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use datafusion::{arrow::datatypes::DataType, logical_expr::Volatility};
+use std::any::Any;
+
+use arrow::{
+ array::{ArrayRef, AsArray, Float64Array},
+ datatypes::Float64Type,
+};
+use datafusion::error::Result;
+use datafusion::prelude::*;
+use datafusion_common::ScalarValue;
+use datafusion_expr::{
+ PartitionEvaluator, Signature, WindowFrame, WindowUDF, WindowUDFImpl,
+};
+
+/// This example shows how to use the full WindowUDFImpl API to implement a
user
+/// defined function. As in the `simple_udwf.rs` example, this struct
implements
Review Comment:
```suggestion
/// defined window function. As in the `simple_udwf.rs` example, this struct
implements
```
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