alamb commented on code in PR #10354:
URL: https://github.com/apache/datafusion/pull/10354#discussion_r1591437235
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
##########
@@ -1307,6 +1309,39 @@ impl<'a, S: SimplifyInfo> TreeNodeRewriter for
Simplifier<'a, S> {
ExprSimplifyResult::Simplified(expr) => Transformed::yes(expr),
},
+ Expr::AggregateFunction(AggregateFunction {
Review Comment:
It seems like in order to be able to make this API avoid copying, it would
need to pass the `distinct`, `filter`, etc fields in and then get them back
Another thing we could do is to use `Transformed` directly
What if we made something like
```rust
struct AggregateFunctionsArgs {
args: Vec<Expr>,
distinct: bool,
filter: Option<Expr>,
order_by: ...
}
```
And then the call to simplify to be
```rust
trait AggreagateUDFImpl {
...
fn simplify(
&self,
agg_args: AggregateFunctionsArgs,
) -> Result<Transformed<AggregateFunctionsArgs> {
Ok(Transformed::no(agg_args))
}
```
##########
datafusion/expr/src/udaf.rs:
##########
@@ -195,6 +197,21 @@ impl AggregateUDF {
pub fn create_groups_accumulator(&self) -> Result<Box<dyn
GroupsAccumulator>> {
self.inner.create_groups_accumulator()
}
+ /// Do the function rewrite
+ ///
+ /// See [`AggregateUDFImpl::simplify`] for more details.
+ pub fn simplify(
+ &self,
+ args: Vec<Expr>,
Review Comment:
One benefit is that we could potentially add new fields without causing an
API change 🤔
Another benefit could be that we could add a default method that recreated
the expression. For example
```rust
impl AggegateArgs {
// recreate the original aggregate fucntions
fn into_expr(self) -> Expr { ... }
...
}
```
Another benefit is, as @jayzhan211 says, that it would be more consistent
with the other APIs
##########
datafusion-examples/examples/simplify_udaf_expression.rs:
##########
@@ -0,0 +1,185 @@
+// 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 arrow_schema::{Field, Schema};
+use datafusion::{arrow::datatypes::DataType, logical_expr::Volatility};
+use datafusion_expr::simplify::SimplifyInfo;
+
+use std::{any::Any, sync::Arc};
+
+use datafusion::arrow::{array::Float32Array, record_batch::RecordBatch};
+use datafusion::error::Result;
+use datafusion::{assert_batches_eq, prelude::*};
+use datafusion_common::cast::as_float64_array;
+use datafusion_expr::{
+ expr::{AggregateFunction, AggregateFunctionDefinition},
+ function::AccumulatorArgs,
+ simplify::ExprSimplifyResult,
+ Accumulator, AggregateUDF, AggregateUDFImpl, GroupsAccumulator, Signature,
+};
+
+/// This example shows how to use the AggregateUDFImpl::simplify API to
simplify/replace user
+/// defined aggregate function with a different expression which is defined in
the `simplify` method.
+
+#[derive(Debug, Clone)]
+struct BetterAvgUdaf {
+ signature: Signature,
+}
+
+impl BetterAvgUdaf {
+ /// Create a new instance of the GeoMeanUdaf struct
+ fn new() -> Self {
+ Self {
+ signature: Signature::exact(vec![DataType::Float64],
Volatility::Immutable),
+ }
+ }
+}
+
+impl AggregateUDFImpl for BetterAvgUdaf {
+ fn as_any(&self) -> &dyn Any {
+ self
+ }
+
+ fn name(&self) -> &str {
+ "better_avg"
+ }
+
+ fn signature(&self) -> &Signature {
+ &self.signature
+ }
+
+ fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
+ Ok(DataType::Float64)
+ }
+
+ fn accumulator(&self, _acc_args: AccumulatorArgs) -> Result<Box<dyn
Accumulator>> {
+ unimplemented!("should not be invoked")
+ }
+
+ fn state_fields(
+ &self,
+ _name: &str,
+ _value_type: DataType,
+ _ordering_fields: Vec<arrow_schema::Field>,
+ ) -> Result<Vec<arrow_schema::Field>> {
+ unimplemented!("should not be invoked")
+ }
+
+ fn groups_accumulator_supported(&self) -> bool {
+ true
+ }
+
+ fn create_groups_accumulator(&self) -> Result<Box<dyn GroupsAccumulator>> {
+ unimplemented!("should not get here");
+ }
+ // we override method, to return new expression which would substitute
+ // user defined function call
+ fn simplify(
+ &self,
+ args: Vec<Expr>,
+ distinct: &bool,
Review Comment:
Given the work we have been doing on
https://github.com/apache/datafusion/issues/9637 let's not add an API that
forces cloning
Another potential thing is to use
[`Transformed`](https://github.com/apache/datafusion/blob/89443bff20015ef6c7646ca32754ece8c4093910/datafusion/common/src/tree_node.rs#L583-L606)
directlt
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