Pandas Series: first() function

Subset initial periods of Pandas time series

The first() function (convenience method ) is used to subset initial periods of time series data based on a date offset.

Syntax:

Series.first(self, offset)

Parameters:

Returns: subset - same type as caller

Raises: TypeError
If the index is not a DatetimeIndex

Example:

Python-Pandas Code:

import numpy as np
import pandas as pd
i = pd.date_range('2019-02-09', periods=4, freq='2D')
ts = pd.DataFrame({'X': [1,2,3,4]}, index=i)
ts

Output:

              X
2019-02-09	1
2019-02-11	2
2019-02-13	3
2019-02-15	4

Example - Get the rows for the first 3 days:

Python-Pandas Code:

import numpy as np
import pandas as pd
i = pd.date_range('2019-02-09', periods=4, freq='2D')
ts = pd.DataFrame({'X': [1,2,3,4]}, index=i)
ts.first('3D')

Output:

              X
2019-02-09	1
2019-02-11	2

Notice the data for 3 first calender days were returned, not the first 3 days observed in the dataset,and therefore data for 2019-02-13 was not returned.

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