Temporal

[Polars Documentation]

OpenDP supports some manipulation of dates and times, which can be useful in predicates and grouping functions.

Python

>>> import polars as pl

>>> import opendp.prelude as dp
>>> dp.enable_features("contrib")

>>> lf_dates = (
...     pl.scan_csv(dp.examples.get_france_lfs_path())
...     # prepare the data with some expressions that are not yet supported in OpenDP
...     .select(
...         DATE=pl.concat_str(
...             "YEAR",
...             pl.col.QUARTER * 3,
...             pl.lit("01"),
...             separator="-",
...         )
...     )
... )

>>> context = dp.Context.compositor(
...     data=lf_dates,
...     privacy_unit=dp.unit_of(contributions=36),
...     privacy_loss=dp.loss_of(epsilon=1.0, delta=1e-7),
...     split_evenly_over=1,
... )

Date/Time Components

• Date expressions (can be applied to pl.Date and pl.Datetime dtypes)

  • .dt.year

  • .dt.iso_year

  • .dt.quarter

  • .dt.month

  • .dt.week

  • .dt.weekday

  • .dt.day

  • .dt.ordinal_day

• Time expressions (can be applied to pl.Time and pl.Datetime dtypes)

  • .dt.hour

  • .dt.minute

  • .dt.second

  • .dt.millisecond

  • .dt.microsecond

  • .dt.nanosecond

An example of their use can be seen below, where a string column is parsed into dates, and then year and month components are retrieved from the dates.

Python

>>> query = (
...     context.query()
...     .with_columns(
...         pl.col.DATE.str.to_date(format=r"%Y-%m-%d")
...     )
...     .with_columns(
...         YEAR=pl.col.DATE.dt.year(),
...         MONTH=pl.col.DATE.dt.month(),
...     )
...     .group_by("YEAR", "MONTH")
...     .agg(dp.len(signed=True))
... )
>>> query.release().collect().sort("YEAR", "MONTH")
shape: (36, 3)
┌──────┬───────┬────────┐
│ YEAR ┆ MONTH ┆ len    │
│ ---  ┆ ---   ┆ ---    │
│ i32  ┆ i8    ┆ i64    │
╞══════╪═══════╪════════╡
│ 2005 ┆ ... ┆ ... │
│ 2005 ┆ ... ┆ ... │
│ 2005 ┆ ... ┆ ... │
│ 2005 ┆ ... ┆ ... │
│ 2006 ┆ ... ┆ ... │
...
│ 2012 ┆ ... ┆ ... │
│ 2013 ┆ ... ┆ ... │
│ 2013 ┆ ... ┆ ... │
│ 2013 ┆ ... ┆ ... │
│ 2013 ┆ ... ┆ ... │
└──────┴───────┴────────┘