pandas过滤条件最近3个月

Question

我想过滤一个熊猫数据框到最近3个月。

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] 

这段代码已经有效，但是有一个月的硬编码为30天。我如何使用pd.Timedelta('-3 month')（看起来不像这样工作）来实现更强大的功能？

Answer 1

我想你需要offsets，因为只有Timedelta不个月的工作：

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]