dask.dataframe.to_datetime

dask.dataframe.to_datetime

dask.dataframe.to_datetime(arg: DatetimeScalar, errors: str = 'raise', dayfirst: bool = False, yearfirst: bool = False, utc: bool | None = None, format: str | None = None, exact: bool = True, unit: str | None = None, infer_datetime_format: bool = False, origin='unix', cache: bool = True) DatetimeScalar | NaTType[source]
dask.dataframe.to_datetime(arg: dask.dataframe.core.Series, errors: str = 'raise', dayfirst: bool = False, yearfirst: bool = False, utc: bool | None = None, format: str | None = None, exact: bool = True, unit: str | None = None, infer_datetime_format: bool = False, origin='unix', cache: bool = True) dask.dataframe.core.Series
dask.dataframe.to_datetime(arg: list | tuple | np.ndarray, errors: str = 'raise', dayfirst: bool = False, yearfirst: bool = False, utc: bool | None = None, format: str | None = None, exact: bool = True, unit: str | None = None, infer_datetime_format: bool = False, origin='unix', cache: bool = True) DatetimeIndex

Convert argument to datetime.

This function converts a scalar, array-like, Series or DataFrame/dict-like to a pandas datetime object.

Parameters
argint, float, str, datetime, list, tuple, 1-d array, Series, DataFrame/dict-like

The object to convert to a datetime. If a DataFrame is provided, the method expects minimally the following columns: "year", "month", "day".

errors{‘ignore’, ‘raise’, ‘coerce’}, default ‘raise’
  • If 'raise', then invalid parsing will raise an exception.

  • If 'coerce', then invalid parsing will be set as NaT.

  • If 'ignore', then invalid parsing will return the input.

dayfirstbool, default False

Specify a date parse order if arg is str or is list-like. If True, parses dates with the day first, e.g. "10/11/12" is parsed as 2012-11-10.

Warning

dayfirst=True is not strict, but will prefer to parse with day first. If a delimited date string cannot be parsed in accordance with the given dayfirst option, e.g. to_datetime(['31-12-2021']), then a warning will be shown.

yearfirstbool, default False

Specify a date parse order if arg is str or is list-like.

  • If True parses dates with the year first, e.g. "10/11/12" is parsed as 2010-11-12.

  • If both dayfirst and yearfirst are True, yearfirst is preceded (same as dateutil).

Warning

yearfirst=True is not strict, but will prefer to parse with year first.

utcbool, default None

Control timezone-related parsing, localization and conversion.

  • If True, the function always returns a timezone-aware UTC-localized Timestamp, Series or DatetimeIndex. To do this, timezone-naive inputs are localized as UTC, while timezone-aware inputs are converted to UTC.

  • If False (default), inputs will not be coerced to UTC. Timezone-naive inputs will remain naive, while timezone-aware ones will keep their time offsets. Limitations exist for mixed offsets (typically, daylight savings), see Examples section for details.

See also: pandas general documentation about timezone conversion and localization.

formatstr, default None

The strftime to parse time, e.g. "%d/%m/%Y". Note that "%f" will parse all the way up to nanoseconds. See strftime documentation for more information on choices.

exactbool, default True

Control how format is used:

  • If True, require an exact format match.

  • If False, allow the format to match anywhere in the target string.

unitstr, default ‘ns’

The unit of the arg (D,s,ms,us,ns) denote the unit, which is an integer or float number. This will be based off the origin. Example, with unit='ms' and origin='unix' (the default), this would calculate the number of milliseconds to the unix epoch start.

infer_datetime_formatbool, default False

If True and no format is given, attempt to infer the format of the datetime strings based on the first non-NaN element, and if it can be inferred, switch to a faster method of parsing them. In some cases this can increase the parsing speed by ~5-10x.

originscalar, default ‘unix’

Define the reference date. The numeric values would be parsed as number of units (defined by unit) since this reference date.

  • If 'unix' (or POSIX) time; origin is set to 1970-01-01.

  • If 'julian', unit must be 'D', and origin is set to beginning of Julian Calendar. Julian day number 0 is assigned to the day starting at noon on January 1, 4713 BC.

  • If Timestamp convertible, origin is set to Timestamp identified by origin.

cachebool, default True

If True, use a cache of unique, converted dates to apply the datetime conversion. May produce significant speed-up when parsing duplicate date strings, especially ones with timezone offsets. The cache is only used when there are at least 50 values. The presence of out-of-bounds values will render the cache unusable and may slow down parsing.

Changed in version 0.25.0: changed default value from False to True.

Returns
datetime

If parsing succeeded. Return type depends on input (types in parenthesis correspond to fallback in case of unsuccessful timezone or out-of-range timestamp parsing):

Raises
ParserError

When parsing a date from string fails.

ValueError

When another datetime conversion error happens. For example when one of ‘year’, ‘month’, day’ columns is missing in a DataFrame, or when a Timezone-aware datetime.datetime is found in an array-like of mixed time offsets, and utc=False.

See also

DataFrame.astype

Cast argument to a specified dtype.

to_timedelta

Convert argument to timedelta.

convert_dtypes

Convert dtypes.

Notes

Many input types are supported, and lead to different output types:

  • scalars can be int, float, str, datetime object (from stdlib datetime module or numpy). They are converted to Timestamp when possible, otherwise they are converted to datetime.datetime. None/NaN/null scalars are converted to NaT.

  • array-like can contain int, float, str, datetime objects. They are converted to DatetimeIndex when possible, otherwise they are converted to Index with object dtype, containing datetime.datetime. None/NaN/null entries are converted to NaT in both cases.

  • Series are converted to Series with datetime64 dtype when possible, otherwise they are converted to Series with object dtype, containing datetime.datetime. None/NaN/null entries are converted to NaT in both cases.

  • DataFrame/dict-like are converted to Series with datetime64 dtype. For each row a datetime is created from assembling the various dataframe columns. Column keys can be common abbreviations like [‘year’, ‘month’, ‘day’, ‘minute’, ‘second’, ‘ms’, ‘us’, ‘ns’]) or plurals of the same.

The following causes are responsible for datetime.datetime objects being returned (possibly inside an Index or a Series with object dtype) instead of a proper pandas designated type (Timestamp, DatetimeIndex or Series with datetime64 dtype):

  • when any input element is before Timestamp.min or after Timestamp.max, see timestamp limitations.

  • when utc=False (default) and the input is an array-like or Series containing mixed naive/aware datetime, or aware with mixed time offsets. Note that this happens in the (quite frequent) situation when the timezone has a daylight savings policy. In that case you may wish to use utc=True.

Examples

Handling various input formats

Assembling a datetime from multiple columns of a DataFrame. The keys can be common abbreviations like [‘year’, ‘month’, ‘day’, ‘minute’, ‘second’, ‘ms’, ‘us’, ‘ns’]) or plurals of the same

>>> df = pd.DataFrame({'year': [2015, 2016],
...                    'month': [2, 3],
...                    'day': [4, 5]})
>>> pd.to_datetime(df)
0   2015-02-04
1   2016-03-05
dtype: datetime64[ns]

Passing infer_datetime_format=True can often-times speedup a parsing if its not an ISO8601 format exactly, but in a regular format.

>>> s = pd.Series(['3/11/2000', '3/12/2000', '3/13/2000'] * 1000)
>>> s.head()
0    3/11/2000
1    3/12/2000
2    3/13/2000
3    3/11/2000
4    3/12/2000
dtype: object
>>> %timeit pd.to_datetime(s, infer_datetime_format=True)  
100 loops, best of 3: 10.4 ms per loop
>>> %timeit pd.to_datetime(s, infer_datetime_format=False)  
1 loop, best of 3: 471 ms per loop

Using a unix epoch time

>>> pd.to_datetime(1490195805, unit='s')
Timestamp('2017-03-22 15:16:45')
>>> pd.to_datetime(1490195805433502912, unit='ns')
Timestamp('2017-03-22 15:16:45.433502912')

Warning

For float arg, precision rounding might happen. To prevent unexpected behavior use a fixed-width exact type.

Using a non-unix epoch origin

>>> pd.to_datetime([1, 2, 3], unit='D',
...                origin=pd.Timestamp('1960-01-01'))
DatetimeIndex(['1960-01-02', '1960-01-03', '1960-01-04'],
              dtype='datetime64[ns]', freq=None)

Non-convertible date/times

If a date does not meet the timestamp limitations, passing errors='ignore' will return the original input instead of raising any exception.

Passing errors='coerce' will force an out-of-bounds date to NaT, in addition to forcing non-dates (or non-parseable dates) to NaT.

>>> pd.to_datetime('13000101', format='%Y%m%d', errors='ignore')
datetime.datetime(1300, 1, 1, 0, 0)
>>> pd.to_datetime('13000101', format='%Y%m%d', errors='coerce')
NaT

Timezones and time offsets

The default behaviour (utc=False) is as follows:

  • Timezone-naive inputs are converted to timezone-naive DatetimeIndex:

>>> pd.to_datetime(['2018-10-26 12:00', '2018-10-26 13:00:15'])
DatetimeIndex(['2018-10-26 12:00:00', '2018-10-26 13:00:15'],
              dtype='datetime64[ns]', freq=None)
  • Timezone-aware inputs with constant time offset are converted to timezone-aware DatetimeIndex:

>>> pd.to_datetime(['2018-10-26 12:00 -0500', '2018-10-26 13:00 -0500'])
DatetimeIndex(['2018-10-26 12:00:00-05:00', '2018-10-26 13:00:00-05:00'],
              dtype='datetime64[ns, pytz.FixedOffset(-300)]', freq=None)
  • However, timezone-aware inputs with mixed time offsets (for example issued from a timezone with daylight savings, such as Europe/Paris) are not successfully converted to a DatetimeIndex. Instead a simple Index containing datetime.datetime objects is returned:

>>> pd.to_datetime(['2020-10-25 02:00 +0200', '2020-10-25 04:00 +0100'])
Index([2020-10-25 02:00:00+02:00, 2020-10-25 04:00:00+01:00],
      dtype='object')
  • A mix of timezone-aware and timezone-naive inputs is converted to a timezone-aware DatetimeIndex if the offsets of the timezone-aware are constant:

>>> from datetime import datetime
>>> pd.to_datetime(["2020-01-01 01:00 -01:00", datetime(2020, 1, 1, 3, 0)])
DatetimeIndex(['2020-01-01 01:00:00-01:00', '2020-01-01 02:00:00-01:00'],
              dtype='datetime64[ns, pytz.FixedOffset(-60)]', freq=None)
  • Finally, mixing timezone-aware strings and datetime.datetime always raises an error, even if the elements all have the same time offset.

>>> from datetime import datetime, timezone, timedelta
>>> d = datetime(2020, 1, 1, 18, tzinfo=timezone(-timedelta(hours=1)))
>>> pd.to_datetime(["2020-01-01 17:00 -0100", d])
Traceback (most recent call last):
    ...
ValueError: Tz-aware datetime.datetime cannot be converted to datetime64
            unless utc=True

Setting utc=True solves most of the above issues:

  • Timezone-naive inputs are localized as UTC

>>> pd.to_datetime(['2018-10-26 12:00', '2018-10-26 13:00'], utc=True)
DatetimeIndex(['2018-10-26 12:00:00+00:00', '2018-10-26 13:00:00+00:00'],
              dtype='datetime64[ns, UTC]', freq=None)
  • Timezone-aware inputs are converted to UTC (the output represents the exact same datetime, but viewed from the UTC time offset +00:00).

>>> pd.to_datetime(['2018-10-26 12:00 -0530', '2018-10-26 12:00 -0500'],
...                utc=True)
DatetimeIndex(['2018-10-26 17:30:00+00:00', '2018-10-26 17:00:00+00:00'],
              dtype='datetime64[ns, UTC]', freq=None)
  • Inputs can contain both naive and aware, string or datetime, the above rules still apply

>>> pd.to_datetime(['2018-10-26 12:00', '2018-10-26 12:00 -0530',
...                datetime(2020, 1, 1, 18),
...                datetime(2020, 1, 1, 18,
...                tzinfo=timezone(-timedelta(hours=1)))],
...                utc=True)
DatetimeIndex(['2018-10-26 12:00:00+00:00', '2018-10-26 17:30:00+00:00',
               '2020-01-01 18:00:00+00:00', '2020-01-01 19:00:00+00:00'],
              dtype='datetime64[ns, UTC]', freq=None)