BPt.Dataset.first#

Dataset.first(offset)[source]#

Select initial periods of time series data based on a date offset.

When having a DataFrame with dates as index, this function can select the first few rows based on a date offset.

Parameters

offsetstr, DateOffset or dateutil.relativedelta: The offset length of the data that will be selected. For instance, ‘1M’ will display all the rows having their index within the first month.

Returns

Series or DataFrame: A subset of the caller.

Raises

TypeError: If the index is not a DatetimeIndex

See also

last: Select final periods of time series based on a date offset.
at_time: Select values at a particular time of the day.
between_time: Select values between particular times of the day.

Examples

>>> i = pd.date_range('2018-04-09', periods=4, freq='2D')
>>> ts = pd.DataFrame({'A': [1, 2, 3, 4]}, index=i)
>>> ts
            A
2018-04-09  1
2018-04-11  2
2018-04-13  3
2018-04-15  4

Get the rows for the first 3 days:

>>> ts.first('3D')
            A
2018-04-09  1
2018-04-11  2

Notice the data for 3 first calendar days were returned, not the first 3 days observed in the dataset, and therefore data for 2018-04-13 was not returned.