Retrieve date from datetime column in polars

Question

Currently when I try to retrieve date from a polars datetime column, I have to write something similar to:

import polars as pl
import datetime as dt

df = pl.DataFrame({
    'time': [dt.datetime.now()]
})

df = df.with_columns(
    pl.col("time").map_elements(lambda x: x.date()).alias("date")
)

shape: (1, 2)
┌────────────────────────────┬────────────┐
│ time                       ┆ date       │
│ ---                        ┆ ---        │
│ datetime[μs]               ┆ date       │
╞════════════════════════════╪════════════╡
│ 2024-07-20 11:41:04.265539 ┆ 2024-07-20 │
└────────────────────────────┴────────────┘

Is there a different way, something closer to:

pl.col("time").dt.date().alias("date")

jqurious · Accepted Answer · 2024-07-21 15:20:24Z

18

You can use .dt.date()

import datetime
import polars as pl

df = pl.DataFrame({
    "time": [datetime.datetime.now()]
})

df.with_columns(
    pl.col("time").dt.date().alias("date")
)

shape: (1, 2)
┌────────────────────────────┬────────────┐
│ time                       ┆ date       │
│ ---                        ┆ ---        │
│ datetime[μs]               ┆ date       │
╞════════════════════════════╪════════════╡
│ 2024-07-21 16:17:41.489579 ┆ 2024-07-21 │
└────────────────────────────┴────────────┘

edited Jul 21, 2024 at 15:20

jqurious

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answered Aug 2, 2022 at 19:23

ritchie46

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1 Comment

David Waterworth Over a year ago

I think this works if "time" is UTC but if it's localized I end up with i.e. 2024-04-01 00:00:00 AEDT (datetime[μs, Australia/Sydney]) being converted to 2024-03-31 (date). I would recomend using .dt.date() not .cast(pl.Date)

Jan Kislinger · Accepted Answer · 2023-03-28 05:44:57Z

8

Since polars version 0.16.15 (released just a few days ago). The code in your question is actually valid.

pl.col("time").dt.date().alias("date")

This is the diff that made it possible. And it works both on pl.Series and pl.Expr (used in lazy data frames).

answered Mar 28, 2023 at 5:44

Jan Kislinger

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2 Comments

Alex Over a year ago

what is stackoverflows procedure to update the question then, do I just add an edit on top?

Jan Kislinger Over a year ago

I don't think you need to change anything :)

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