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# Description
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This PR lifts the constraint that expressions in the `polars group-by`
command must be limited only to the type `Expr::Column` rather than most
`Expr` types, which is what the underlying polars crate allows. This
change enables more complex expressions to group by.
In the example below, we group by even or odd days of column `a`. While
we can reach the same result by creating and grouping by a new column in
two separate steps, integrating these steps in a single group-by allows
for better delegation to the polars optimizer.
```nushell
# Group by an expression and perform an aggregation
> [[a b]; [2025-04-01 1] [2025-04-02 2] [2025-04-03 3] [2025-04-04 4]]
| polars into-lazy
| polars group-by (polars col a | polars get-day | $in mod 2)
| polars agg [
(polars col b | polars min | polars as "b_min")
(polars col b | polars max | polars as "b_max")
(polars col b | polars sum | polars as "b_sum")
]
| polars collect
| polars sort-by a
╭───┬───┬───────┬───────┬───────╮
│ # │ a │ b_min │ b_max │ b_sum │
├───┼───┼───────┼───────┼───────┤
│ 0 │ 0 │ 2 │ 4 │ 6 │
│ 1 │ 1 │ 1 │ 3 │ 4 │
╰───┴───┴───────┴───────┴───────╯
```
# User-Facing Changes
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helps us keep track of breaking changes. -->
No breaking changes. The user is empowered to use more complex
expressions in `polars group-by`
# Tests + Formatting
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> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
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> toolkit check pr
> ```
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An example is added to `polars group-by`.
# After Submitting
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| .. | ||
| src | ||
| Cargo.toml | ||
| LICENSE | ||