mbrobbel opened a new pull request #11937:
URL: https://github.com/apache/arrow/pull/11937
Initially I tried to implement this as a `ScalarAggregateFunction` (as
suggested in the issue), however given that there is no way to express
sensitivity to order, it's currently not possible to correctly implement the
`ScalarAggregator::MergeFrom` function. This is now implemented as a
`VectorFunction`.
I'm still working on supporting more types:
- [x] Booleans
- [x] Signed and unsigned integer types
- [ ] Floating point types (I'm trying to figure out what I can re-use)
- [ ] Temporal types
- [ ] Decimal types
I'll create two follow-up JIRA issues to:
- Add support for UTF8 arrays (via lexicographical order):
```
Input: utf8
[
"a",
"b",
"c"
]
Output: struct<increasing:boolean, strictly_decreasing:boolean,
decreasing:boolean, strictly_decreasing:boolean>
{increasing: true, strictly_increasing: true, decreasing: false,
strictly_decreasing: false}
```
- Implement this function for list arrays with well-ordered element types:
```
Input: list<uint8>
[
[1, 2, 3],
[3, 3, 2],
[1, 2, 1, 2]
]
Output list<struct<increasing:boolean, strictly_decreasing:boolean,
decreasing:boolean, strictly_decreasing:boolean>>
[
{increasing: true, strictly_increasing: true, decreasing: false,
strictly_decreasing: false},
{increasing: false, strictly_increasing: false, decreasing: true,
strictly_decreasing: false},
{increasing: false, stirctly_increasing: false, decreasing: false,
strictly_decreasing: false}
]
```
cc @bkietz
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