alamb commented on code in PR #14699:
URL: https://github.com/apache/datafusion/pull/14699#discussion_r1966510247
##########
datafusion/physical-expr-common/src/physical_expr.rs:
##########
@@ -144,6 +153,111 @@ pub trait PhysicalExpr: Send + Sync + Display + Debug +
DynEq + DynHash {
Ok(Some(vec![]))
}
+ /// Computes the output statistics for the expression, given the input
+ /// statistics.
+ ///
+ /// # Parameters
+ ///
+ /// * `children` are the statistics for the children (inputs) of this
+ /// expression.
+ ///
+ /// # Returns
+ ///
+ /// A `Result` containing the output statistics for the expression in
+ /// case of success, or an error object in case of failure.
+ ///
+ /// Expressions (should) implement this function and utilize the
independence
+ /// assumption, match on children distribution types and compute the output
+ /// statistics accordingly. The default implementation simply creates an
+ /// unknown output distribution by combining input ranges. This logic loses
+ /// distribution information, but is a safe default.
+ fn evaluate_statistics(&self, children: &[&StatisticsV2]) ->
Result<StatisticsV2> {
Review Comment:
That makes sense
Therefore I recommend renaming `StatisticsV2` to `Distribution`
This seems farily natural given that all the sub variants are actually
alread named "XYZDistribution" such as `UniformDistribution`,
`ExponentialDistribution`, etc.
For example this seems more consistent:
```rust
pub enum Distribution {
Uniform(UniformDistribution),
Exponential(ExponentialDistribution),
Gaussian(GaussianDistribution),
Bernoulli(BernoulliDistribution),
Unknown(UnknownDistribution),
}
```
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