List columns in Python

A column can hold lists, and the list namespace works on them element-wise.

import polars as pl

frame = pl.DataFrame({
    "lang": ["python", "rust"],
    "tours": [["basics", "pandas", "sklearn"], ["basics", "traits"]],
})

print(frame.with_columns(
    pl.col("tours").list.len().alias("count"),
    pl.col("tours").list.first().alias("first"),
    pl.col("tours").list.join(", ").alias("joined"),
))
print(frame.explode("tours"))

How it works

group_by().agg without a reducer produces list columns.
list.len, list.first and list.eval operate inside each list.
explode turns each element back into its own row.

Keywords and builtins used here

as
print

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Step 2 of 3 in Text, lists & structs, step 21 of 32 in Polars.

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