pandas過濾條件最近3個月

Question

我想過濾一個熊貓數據框到最近3個月。

import pandas as pd 
dates = pd.DataFrame(['2016-11-01', '2016-12-01', '2017-01-01', '2017-02-01', '2017-03-01'], columns=['date']) 
dates.date = pd.DatetimeIndex(dates.date) 
import datetime 
today = datetime.date.today() 
first = today.replace(day=1) 
lastMonth = first - datetime.timedelta(days=90) 
print (lastMonth.strftime("%Y-%m")) 
dates[dates.date >= lastMonth] 

這段代碼已經有效，但是有一個月的硬編碼爲30天。我如何使用pd.Timedelta('-3 month')（看起來不像這樣工作）來實現更強大的功能？

Answer 1

我想你需要offsets，因爲只有Timedelta不個月的工作：

lastMonth = first - pd.offsets.MonthBegin(3) 
#lastMonth = first - pd.offsets.relativedelta(months=3) 

---

lastMonth = first - pd.Timedelta(months=3) 

ValueError: cannot construct a Timedelta from the passed arguments, allowed keywords are [weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds]