feat(expr-ir): Finish* implementing ArrowExpr
#3325
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Quite odd behavior for scalar lol
Will come back to this later to shrink
Discovered while adding `kurtosis` test which had an empty series
Adding the `skew` test revealed this "edge case"
The rest will allow them to be used in `group_by`
Indirectly adds support for `over` too, but haven't added tests yet
- Still needs tests - Also unsure what the scalar behavior should be for `mode_all`
I wanna try rewriting this without `numpy` after getting the tests in place
Got quite a few more ideas to experiment with
Each of these are expensive + this version is simpler
Managed to write it with one less `if_else`, but the readability suffered so this will do
dangotbanned
commented
Nov 26, 2025
Much clearer what each case is testing, covers a slightly more, + generates nice test ids
Using `repr` was making the tests *look* like they worked, but the reality was hairier
Solved *some* of my woes - but it looks like there may be another issue?
At least the expansion worked!
Was already working, but always good to be sure
- Expecting a failure for `<15.0`, just not sure what it'll be - `unify_dictionaries` may also be new?
- Needed to rethink the typing a bit - Accessor methods can return `Expr` or `Scalar` and may not depend on the input shape - Also, probably found a bug in `polars` - Nice to see things held together over here 😄
Mostly typing, but generally things that made sense in an earlier version
- `fill_nan`, `null_count` are on `main` - the other two are 2/3 of #3028
a mix of things: - added after the dsl was written - or deprecated before - or not support in `pyarrow` - or I missed it oops
Realized after writing this that I didn't test it https://github.com/narwhals-dev/narwhals/pull/3332/files#r2572340215
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Related issues
ExprIR #2572Description
Note
TODO: List all the new/reimplemented stuff
This PR is a bit of an amuse-bouche.
I've really tried to focus on getting an implementation for all of the methods in the
Exprnamespace. Man there a lot of them nowStill need to catch up with new stuff on
mainthat wasn't there when I started 😅Planning to tackle that after the
Expraccessor methodsSide Note
I'm fighting the urge pretty hard to rewrite how this version of
CompliantExprworks.Most of what is in (https://github.com/narwhals-dev/narwhals/blob/ce3ec2194e1f67e998c3ea1f989e624aadb05b55/narwhals/_plan/arrow/expr.py) is general visitor logic which would be a slog to repeat in every backend.
It works and I'm finding it easy to reason about, but I 100% plan to put in some more design work.
Just need to endure the pain of doing it the long way for the rest of the
Exprnamespace ops 😭