polars.Expr.dt.truncate#

Expr.dt.truncate(every: str | dt.timedelta | Expr) → Expr[source]#

Divide the date/datetime range into buckets.

Each date/datetime is mapped to the start of its bucket using the corresponding local datetime. Note that weekly buckets start on Monday. Ambiguous results are localised using the DST offset of the original timestamp - for example, truncating '2022-11-06 01:30:00 CST' by '1h' results in '2022-11-06 01:00:00 CST', whereas truncating '2022-11-06 01:30:00 CDT' by '1h' results in '2022-11-06 01:00:00 CDT'.

Parameters:
every

Every interval start and period length

Returns:
Expr

Expression of data type Date or Datetime.

Notes

The every argument is created with the the following string language:

  • 1ns (1 nanosecond)

  • 1us (1 microsecond)

  • 1ms (1 millisecond)

  • 1s (1 second)

  • 1m (1 minute)

  • 1h (1 hour)

  • 1d (1 calendar day)

  • 1w (1 calendar week)

  • 1mo (1 calendar month)

  • 1q (1 calendar quarter)

  • 1y (1 calendar year)

These strings can be combined:

  • 3d12h4m25s # 3 days, 12 hours, 4 minutes, and 25 seconds

By “calendar day”, we mean the corresponding time on the next day (which may not be 24 hours, due to daylight savings). Similarly for “calendar week”, “calendar month”, “calendar quarter”, and “calendar year”.

Examples

>>> from datetime import timedelta, datetime
>>> df = (
...     pl.datetime_range(
...         datetime(2001, 1, 1),
...         datetime(2001, 1, 2),
...         timedelta(minutes=225),
...         eager=True,
...     )
...     .alias("datetime")
...     .to_frame()
... )
>>> df
shape: (7, 1)
┌─────────────────────┐
│ datetime            │
│ ---                 │
│ datetime[μs]        │
╞═════════════════════╡
│ 2001-01-01 00:00:00 │
│ 2001-01-01 03:45:00 │
│ 2001-01-01 07:30:00 │
│ 2001-01-01 11:15:00 │
│ 2001-01-01 15:00:00 │
│ 2001-01-01 18:45:00 │
│ 2001-01-01 22:30:00 │
└─────────────────────┘
>>> df.select(pl.col("datetime").dt.truncate("1h"))
shape: (7, 1)
┌─────────────────────┐
│ datetime            │
│ ---                 │
│ datetime[μs]        │
╞═════════════════════╡
│ 2001-01-01 00:00:00 │
│ 2001-01-01 03:00:00 │
│ 2001-01-01 07:00:00 │
│ 2001-01-01 11:00:00 │
│ 2001-01-01 15:00:00 │
│ 2001-01-01 18:00:00 │
│ 2001-01-01 22:00:00 │
└─────────────────────┘
>>> truncate_str = df.select(pl.col("datetime").dt.truncate("1h"))
>>> truncate_td = df.select(pl.col("datetime").dt.truncate(timedelta(hours=1)))
>>> truncate_str.equals(truncate_td)
True

>>> df = (
...     pl.datetime_range(
...         datetime(2001, 1, 1), datetime(2001, 1, 1, 1), "10m", eager=True
...     )
...     .alias("datetime")
...     .to_frame()
... )
>>> df.select(
...     "datetime", pl.col("datetime").dt.truncate("30m").alias("truncate")
... )
shape: (7, 2)
┌─────────────────────┬─────────────────────┐
│ datetime            ┆ truncate            │
│ ---                 ┆ ---                 │
│ datetime[μs]        ┆ datetime[μs]        │
╞═════════════════════╪═════════════════════╡
│ 2001-01-01 00:00:00 ┆ 2001-01-01 00:00:00 │
│ 2001-01-01 00:10:00 ┆ 2001-01-01 00:00:00 │
│ 2001-01-01 00:20:00 ┆ 2001-01-01 00:00:00 │
│ 2001-01-01 00:30:00 ┆ 2001-01-01 00:30:00 │
│ 2001-01-01 00:40:00 ┆ 2001-01-01 00:30:00 │
│ 2001-01-01 00:50:00 ┆ 2001-01-01 00:30:00 │
│ 2001-01-01 01:00:00 ┆ 2001-01-01 01:00:00 │
└─────────────────────┴─────────────────────┘