Get Rows Using Pandas Series First Method

The pandas series.first() method is supposed to return initial periods based on the dates. By applying this method we can get the initial periods of the time series data based on a date offset.

It has a parameter called offset and also we can mention the length of the offset data to select the rows within the limit.

The first() method will return a now Series object with resultant rows and it will raise the TypeError if the index of the input series object doesn’t have the DatetimeIndex.

Example 1

In this following example, a series “s” is created by using the pandas DateTime index with the month name corresponding to the index.

# importing packages
import pandas as pd

# creating dates
dates = pd.date_range('2021-08-15', periods=10, freq='m')

#creating pandas Series with date index
s = pd.Series(dates.strftime('%b'), index= dates)
print (s)

# get the rows by using first method
result = s.first('1M')
print('Result:')
print(result)

Explanation

Here, we applied the first() method with offset “1M” to get the rows within one month.

Output

The output is as follows −

2021-08-31    Aug
2021-09-30    Sep
2021-10-31    Oct
2021-11-30    Nov
2021-12-31    Dec
2022-01-31    Jan
2022-02-28    Feb
2022-03-31    Mar
2022-04-30    Apr
2022-05-31    May
Freq: M, dtype: object

Result:
2021-08-31    Aug
2021-09-30    Sep
Freq: M, dtype: object

We can see both the series objects, the first one is the original series object and the second one resultant series object. Here, we got the resultant series with 2 rows.

Example 2

In the same way, we have created a pandas object with pandas DateTime index. After that, we try to get rows that are having their index within 3 months.

# importing packages
import pandas as pd

# creating dates
dates = pd.date_range('2021-01-20', periods=10, freq='2W')

#creating pandas Series with date index
s = pd.Series(dates.strftime('%b'), index= dates)
print (s)

# get the rows by using first method
result = s.first('3M')
print('Result:')
print(result)

Output

The output is as follows −

2021-01-24    Jan
2021-02-07    Feb
2021-02-21    Feb
2021-03-07    Mar
2021-03-21    Mar
2021-04-04    Apr
2021-04-18    Apr
2021-05-02    May
2021-05-16    May
2021-05-30    May
Freq: 2W-SUN, dtype: object

Result:
2021-01-24    Jan
2021-02-07    Feb
2021-02-21    Feb
2021-03-07    Mar
2021-03-21    Mar
Freq: 2W-SUN, dtype: object

The first method has successfully returned the new series object with 5 rows of data. And all these 5 rows have the index within the first 3 months.