merge函数使用:
http://pandas.pydata.org/pandas-docs/stable/merging.html
timestamp解释:瘳雪峰
Datetimes and Timedeltas:
https://docs.scipy.org/doc/numpy/reference/arrays.datetime.html
timedelta64帮助完善Datetimes功能,实现日期的基本运算,如:
>>> np.datetime64('2009-01-01') - np.datetime64('2008-01-01')
numpy.timedelta64(366,'D')
>>> np.datetime64('2009') + np.timedelta64(20, 'D')
numpy.datetime64('2009-01-21')
>>> np.timedelta64(1,'W') / np.timedelta64(1,'D')
7.0
>>> lambda x: x/np.timedelta64(1,'D')
>可以将datime64日期类型数据通过timedelta64转换为数字格式