Using `filter` inside `summarise` raises with an `ArgumentError`

[billylanchantin]

Explorer Issue #1115 (Livebook Contents)

Mix.install([
  {:explorer, "~> 0.11.0"},
  {:kino_pythonx, "~> 0.1.0"},
  {:pythonx, "~> 0.4.2"},
])

[project]
name = "project"
version = "0.0.0"
requires-python = "==3.13.*"
dependencies = [
  "polars==1.32.3"
]

Data

data = %{
  a: [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4],
  b: [99, 1, 1, 99, 99, 99, 1, 1, 1, 1, 99, 99]
}

%{a: [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4], b: [99, 1, 1, 99, 99, 99, 1, 1, 1, 1, 99, 99]}

Python

import polars as pl

df_polars = (
    pl.DataFrame(data)
    .group_by(pl.col("a"))
    .agg(pl.col("b").filter(pl.col("b") > 40).mean())
)

df_polars

#Pythonx.Object<
  shape: (4, 2)
  ┌─────┬──────┐
  │ a   ┆ b    │
  │ --- ┆ ---  │
  │ i64 ┆ f64  │
  ╞═════╪══════╡
  │ 3   ┆ 99.0 │
  │ 2   ┆ 99.0 │
  │ 1   ┆ 99.0 │
  │ 4   ┆ 99.0 │
  └─────┴──────┘
>

Elixir

require Explorer.DataFrame, as: DF

df_explorer =
  data
  |> DF.new()
  |> DF.group_by("a")
  |> DF.summarise(b |> filter(_ > 40) |> mean)

** (ArgumentError) expected a variable to be given to var!, got: Explorer.DataFrame.pull(var!(df, Explorer.Query), :df)
    (elixir 1.18.3) expanding macro: Kernel.var!/2
    #cell:pfefn52y4pwggjrl:7: (file)
    (explorer 0.11.0) expanding macro: Explorer.Query.query/1
    #cell:pfefn52y4pwggjrl:7: (file)
    (elixir 1.18.3) expanding macro: Kernel.|>/2
    #cell:pfefn52y4pwggjrl:7: (file)
    (elixir 1.18.3) expanding macro: Kernel.|>/2
    #cell:pfefn52y4pwggjrl:7: (file)