EdsonPetry opened a new pull request, #23265:
URL: https://github.com/apache/datafusion/pull/23265
## Which issue does this PR close?
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We generally require a GitHub issue to be filed for all bug fixes and
enhancements and this helps us generate change logs for our releases.
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- N/A. No dedicated tracking issue; this adds a single self-contained
higher-order array function. Happy to file one if preferred.
## Rationale for this change
DataFusion already provides higher-order array functions such as
`array_any_match`, `array_filter`, and `array_transform`, but there is no
direct way to retrieve the *first* element of an array that satisfies a
predicate. Today this requires `array_filter` followed by `array_element(...,
1)`, which materializes an intermediate filtered array. `array_first` expresses
this directly and rounds out the set of lambda-based array functions.
## What changes are included in this PR?
- New higher-order function `array_first(array, predicate)` (alias
`list_first`) in `datafusion-functions-nested`, returning the first element for
which the lambda predicate returns `true`:
- returns `null` when the array is empty or no element matches;
- a predicate that evaluates to `null` for an element is treated as not
matching;
- a matched element that is itself `null` is returned as `null`.
- Implemented as a `HigherOrderUDFImpl` following the existing array-lambda
functions, including the standard fast paths (fully-null input) and correct
handling of sliced lists, null sublists, and captured outer columns.
- Registration in `functions-nested` (`expr_fn` re-export and the default
higher-order function list).
- Unit tests, sqllogictest coverage, and regenerated SQL function
documentation.
## Are these changes tested?
Yes:
- Unit tests in `array_first.rs` covering match/no-match, empty and null
arrays, null-predicate handling, matched-null elements, sliced lists, captured
outer columns, and non-primitive element types.
- sqllogictest cases in `test_files/array/array_first.slt`, including
`LargeList` and the `list_first` alias.
## Are there any user-facing changes?
Yes. A new array function `array_first` (alias `list_first`) is available in
SQL, with generated documentation under the Array Functions section. There are
no breaking changes to existing public APIs.
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