Trait datafusion::logical_expr::WindowUDFImpl
source · pub trait WindowUDFImpl: Debug + Send + Sync {
// Required methods
fn as_any(&self) -> &(dyn Any + 'static);
fn name(&self) -> &str;
fn signature(&self) -> &Signature;
fn return_type(
&self,
arg_types: &[DataType],
) -> Result<DataType, DataFusionError>;
fn partition_evaluator(
&self,
) -> Result<Box<dyn PartitionEvaluator>, DataFusionError>;
// Provided methods
fn aliases(&self) -> &[String] { ... }
fn simplify(
&self,
) -> Option<Box<dyn Fn(WindowFunction, &dyn SimplifyInfo) -> Result<Expr, DataFusionError>>> { ... }
}
Expand description
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.
§Basic Example
#[derive(Debug, Clone)]
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 partition_evaluator(&self) -> Result<Box<dyn PartitionEvaluator>> { unimplemented!() }
}
// Create a new WindowUDF 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(None),
);
Required Methods§
sourcefn signature(&self) -> &Signature
fn signature(&self) -> &Signature
Returns the function’s Signature
for information about what input
types are accepted and the function’s Volatility.
sourcefn return_type(
&self,
arg_types: &[DataType],
) -> Result<DataType, DataFusionError>
fn return_type( &self, arg_types: &[DataType], ) -> Result<DataType, DataFusionError>
What DataType
will be returned by this function, given the types of
the arguments
sourcefn partition_evaluator(
&self,
) -> Result<Box<dyn PartitionEvaluator>, DataFusionError>
fn partition_evaluator( &self, ) -> Result<Box<dyn PartitionEvaluator>, DataFusionError>
Invoke the function, returning the PartitionEvaluator
instance
Provided Methods§
sourcefn aliases(&self) -> &[String]
fn aliases(&self) -> &[String]
Returns any aliases (alternate names) for this function.
Note: aliases
should only include names other than Self::name
.
Defaults to []
(no aliases)
sourcefn simplify(
&self,
) -> Option<Box<dyn Fn(WindowFunction, &dyn SimplifyInfo) -> Result<Expr, DataFusionError>>>
fn simplify( &self, ) -> Option<Box<dyn Fn(WindowFunction, &dyn SimplifyInfo) -> Result<Expr, DataFusionError>>>
Optionally apply per-UDWF simplification / rewrite rules.
This can be used to apply function specific simplification rules during optimization. The default implementation does nothing.
Note that DataFusion handles simplifying arguments and “constant
folding” (replacing a function call with constant arguments such as
my_add(1,2) --> 3
). Thus, there is no need to implement such
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
§Returns
None if simplify is not defined or,
Or, a closure with two arguments:
- ‘window_function’: crate::expr::WindowFunction for which simplified has been invoked
- ‘info’: crate::simplify::SimplifyInfo