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Posted to github@arrow.apache.org by "jayzhan211 (via GitHub)" <gi...@apache.org> on 2024/02/18 12:47:55 UTC
[I] Comparison for nested type [arrow-rs]
jayzhan211 opened a new issue, #5407:
URL: https://github.com/apache/arrow-rs/issues/5407
**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
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I want to be able to compare ListArray. The comparison order is left to right and if the prefix is the same then it is considered.
lesser.
For example,
* List(1,2,3) < List(1,2,3,4)
* List(List(1,2,3), List(10)) < List(List(1,2,4), List(1))
* List(List(1,2,3), List(1)) > List(List(1,2,2), List(2))
> The behavior takes Duckdb's array sort as a reference.
**Describe the solution you'd like**
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Support nested types in `compare_op`, currently failed on this line.
```rust
if l_t != r_t || l_t.is_nested() {
return Err(ArrowError::InvalidArgumentError(format!(
"Invalid comparison operation: {l_t} {op} {r_t}"
)));
}
```
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We can support most of the ops in the future, `lt` and `eq` are two important functions that should work first.
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Re: [I] Comparison for nested type [arrow-rs]
Posted by "jayzhan211 (via GitHub)" <gi...@apache.org>.
jayzhan211 commented on issue #5407:
URL: https://github.com/apache/arrow-rs/issues/5407#issuecomment-2184954842
> I'm not sure we want to support this within these kernels, in particular the null behaviour is not well-defined. I added support to the comparator for this, which will allow systems like DataFusion to define an ordering for nulls based on a config setting, as Spark and Postgres use different ordering.
>
> There is an example of this here - https://docs.rs/arrow-ord/latest/arrow_ord/ord/fn.make_comparator.html#postgres-compatible-nested-comparison
>
> This will also make it more obvious that the nested comparison is not vectorised
>
> Edit: Filed #5942 to make this more discoverable
Are you suggesting that if datafusion requires nested comparison, we could implement them in datafusion with `make_comparator` like what I had done? Arrow-rs only need support the `make_comparator` kernel for nested type?
https://github.com/apache/datafusion/blob/d32747d09add5e1c670aa32fbe3294ecee15e3b7/datafusion/physical-expr/src/expressions/datum.rs#L28-L58
This is the code that utilize `compare_op`, and nested type is missing
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Re: [I] Comparison for nested type [arrow-rs]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on issue #5407:
URL: https://github.com/apache/arrow-rs/issues/5407#issuecomment-2184915993
I'm not sure we want to support this within these kernels, in particular the null behaviour is not well-defined. I added support to the comparator for this, which will allow systems like DataFusion to define an ordering for nulls based on a config setting, as Spark and Postgres use different ordering.
This will also make it more obvious that the nested comparison is not vectorised
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Re: [I] Comparison for nested type [arrow-rs]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on issue #5407:
URL: https://github.com/apache/arrow-rs/issues/5407#issuecomment-2184969909
Yes, DataFusion should decide what null semantics it wants / make this configurable, and implement it using make_comparator if appropriate
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Re: [I] Comparison for nested type [arrow-rs]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold closed issue #5407: Comparison for nested type
URL: https://github.com/apache/arrow-rs/issues/5407
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