import polars as pl

from datetime import date

​

df = pl.DataFrame(

    {

        "user": [1, 1, 1, 1, 1, 2, 2, 2, 2, 2],

        "date": [

            date(2015, 1, 11),

            date(2015, 1, 11),

            date(2015, 5, 8),

            date(2015, 7, 8),

            date(2016, 3, 18),

            date(2015, 2, 10),

            date(2015, 9, 8),

            date(2016, 1, 1),

            date(2016, 1, 1),

            date(2016, 3, 17),

        ],

    }

)

​

df = df.with_column(pl.col("date").

               rank(method="min").

               over(["user"]).alias("rank"))

​

​

​

​

>>> df

shape: (10, 3)

┌──────┬────────────┬──────┐

│ user ┆ date       ┆ rank │

│ ---  ┆ ---        ┆ ---  │

│ i64  ┆ date       ┆ u32  │

╞══════╪════════════╪══════╡

│ 1    ┆ 2015-01-11 ┆ 1    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 1    ┆ 2015-01-11 ┆ 1    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 1    ┆ 2015-05-08 ┆ 3    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 1    ┆ 2015-07-08 ┆ 4    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ ...  ┆ ...        ┆ ...  │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 2    ┆ 2015-09-08 ┆ 2    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 2    ┆ 2016-01-01 ┆ 3    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 2    ┆ 2016-01-01 ┆ 3    │

├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┤

│ 2    ┆ 2016-03-17 ┆ 5    │

└──────┴────────────┴──────┘