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Posted to github@arrow.apache.org by "alamb (via GitHub)" <gi...@apache.org> on 2024/03/30 20:55:44 UTC
[I] Request: Improve Monotoniciy API [arrow-datafusion]
alamb opened a new issue, #9879:
URL: https://github.com/apache/arrow-datafusion/issues/9879
### Is your feature request related to a problem or challenge?
While reviewing https://github.com/apache/arrow-datafusion/pull/9869 from @tinfoil-knight I was confused about the [`ScalarUDFImpl::monotonicity`](https://docs.rs/datafusion/latest/datafusion/logical_expr/trait.ScalarUDFImpl.html#method.monotonicity) API
```rust
// This function specifies monotonicity behaviors for User defined scalar functions.
fn monotonicity(&self) -> Result<Option<Vec<Option<bool>>>, DataFusionError> {..}
```
The challenge is the cognative complexity of understanding what `Result<Option<Vec<Option<bool>>>` means
The actual code is defined in terms `FuncMonotonicity` https://github.com/apache/arrow-datafusion/blob/57c0bc65280c467ef6f5a498c6e78a616401b286/datafusion/expr/src/signature.rs#L350-L356
However, since it is a typedef it doesn't show up in the Rust docs
### Describe the solution you'd like
An easy to understand Monotonicity API
### Describe alternatives you've considered
I think it would be great to have an API like this:
```rust
// This function specifies monotonicity behaviors for User defined scalar functions.
fn monotonicity(&self) -> Result<Monotonicity>, DataFusionError> {..}
```
And then we could make `Monotonicity` an enum that captured the relevant data. This would both be easier to understand and likely more efficient as well
Something like
```rust
/// Monotonicity of a function with respect to its arguments.
///
/// A function is [monotonic] if it preserves the relative order of its inputs.
///
/// [monotonic]: https://en.wikipedia.org/wiki/Monotonic_function
pub enum Monotonicity {
/// not monotonic or unknown monotonicity
None,
/// Increasing with respect to all of its arguments
Increasing,
/// Decreasing with respect to all of its arguments
Decreasing,
/// Each element of this vector corresponds to an argument and indicates whether
/// the function's behavior is monotonic, or non-monotonic/unknown for that argument, namely:
/// - `None` signifies unknown monotonicity or non-monotonicity.
/// - `Some(true)` indicates that the function is monotonically increasing w.r.t. the argument in question.
/// - Some(false) indicates that the function is monotonically decreasing w.r.t. the argument in question.
Mixed(Vec<bool>),
}
```
I think this would be much eaiser to reason about
### Additional context
_No response_
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Re: [I] Request: Improve Monotoniciy API [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #9879: Request: Improve Monotoniciy API
URL: https://github.com/apache/datafusion/issues/9879
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Re: [I] Request: Improve Monotoniciy API [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on issue #9879:
URL: https://github.com/apache/datafusion/issues/9879#issuecomment-2122335700
https://github.com/apache/datafusion/pull/10504 introduces a new API for boundary propagation, so the API challenge described in this ticket is no longer relevant. Thus closing
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Re: [I] Request: Improve Monotoniciy API [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #9879: Request: Improve Monotoniciy API
URL: https://github.com/apache/datafusion/issues/9879
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Re: [I] Request: Improve Monotoniciy API [arrow-datafusion]
Posted by "tinfoil-knight (via GitHub)" <gi...@apache.org>.
tinfoil-knight commented on issue #9879:
URL: https://github.com/apache/arrow-datafusion/issues/9879#issuecomment-2028467872
take
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